The case-bearer Coleophora serratella L. is a pest, the larvae of which are mining the leaves of birch, alder, hazel, etc. The spectrum of its parasitoids was investigated in the course of its biological control in the territory of Canada and USA, where it was brought from Europe in the thirties and where it caused extensive clear-eating. In the years 1992 and 1993 in the area with local gradation of the case-bearer (Forest Administration Decinsky Sneznik, Northern Bohemia) cases with larvae were collected at the end of May which terminated their development and pupated in the undergrowth vegetation. Single cases with larvae were put into test-tubes to investigate the phenology of eclosion, abundance of the case-bearer and its parasitoids. The length, width and height of the cases produced by the larvae of the fourth instar after wintering were measured in dependence upon the species of parasitoids and the values were compared with the unparasitized cases. The rates of parasitization of the case-bearer amounted to 56.0% (1992) and 38.1% (1993) in natural conditions, in laboratory raising of the case-bearer transferred from the vegetation cover in the stage of the second instar before the beginning of the growing season, the rate of parasitization were lower, 41.0% (1992) and 28.6% (1993). A complex of parasitoids of the case-bearer based on the hitherto studies performed in Europe and Canada involves data on 24 species of ichneumon flies, 23 species of braconids and 19 species of chalcid flies. Ten species were included in a list of the braconids parasitizing on the case-bearer in which the food bond is little probable. The species spectrum of parasitoids in the investigated area in this paper (Tab. I) involves seven species of ichneumon flies, out of which Campoplex borealis** Zett. (1992) and Bathythrix thomsoni** Kerr. (1993) has a dominant position. There were five species of the braconids with the dominant position of the species Agathis mediator** Nz. (20.2%) and Apanteles corvinus** Reinh. (13.1%). The chalcid flies were found only in 1992 (four species). In 1993 overall parasitization decreased and changes were also observed in the composition of the parasitoid fauna of the case-bearer. The braconids A. mediator (22.9%) and A. corvinus (21.9%) continued to be dominant species. Increased abundance was observed in the species Agathis pumila** Ratz. (14.6%) and B. thomsoni (14.6%). The major part of the parasitic complex of ichneumon flies and braconids (C. borealis, Dolichogenidea mesoxanthus** Rusch., A. corvinus, A. mediator) attacks the host in the first developmental instars in the fall, winters in the host and the end of their development is synchronized with the hosts development. All the identified species have one generation within the year. A. corvinus and Campoplex punctipleuris** Horst. are mentioned as new species in the Czech Republic, and in the species B. thomsoni and A. pumila (in Europe) the food bond to the case-bearer Coleophora serratella L. has not been observed until now. The case-bearer, which terminates its development in the second half of May depending upon the climatic conditions, is swarming from the beginning of June to mid-July, while swarming peak is at the end of June. In the complex of parasitoids, the ichneumon files were represented evenly by the low population density from late May to mid-July. The highest population density of the braconids was recorded in the first half of July. The chalcids were swarming in June without expressive culmination, ten days before the swarming peak of the case-bearer (Fig. 2). Measurements of the length, height and width of unparasitized cases of the case-bearer and of the cases with a parasitoid indicated in general that all the three dimensions of parasitized cases were smaller than the average values of unparasitized cases (7.93 mm in length, 2.28 mm in height, 1.88 in width), The dimensions of the cases parasitized by the ichneumon flies (7.76; 2.10; 1.61 mm), chalcids (7.50; 1.97; 1.66 mm) and braconids (7.13; 1.91; 1.61 mm) (Tab. V). The flight hole is a typical trait of some species of parasitoids. The braconids leave the host's case in the same way as an emerging moth, without any injury of the case. Only B. osculator** makes one to two flight holes 0.9 mm in diameter in the case wall which are situated mostly in the upper part of the case, sometimes in its lower part. The cases of the case-bearer parasitized by the ichneumon flies had a flight hole which is larger in the females than in the males. In the species B. thomsoni the flight holes are evenly placed in the basal and apical third of the case, 1.15 mm in diameter in the females and 1.11 mm in the males. In the species C. borealis the females make the flight hole exclusively under the apical part of the case while in the males the flight holes were found both near the basal and apical part of the case, being 0.90 mm in diameter. The flight hole of the species C. punctipleuris was in the apical part of the case (0.77 mm). In the representatives of the genus Gelis sp. the flight hole after emergence of the females is conspicuously large (1.34 mm in G. cinctus, 1.28 mm in G. proximus), and it is mostly situated in the apical part of the case. The chalcids usually make flight holes on the sides of the case in its apical part (Tab. V). none