The effectiveness of releases of ectoparasite Diglyphus isaea to control the three leafminer species infesting chrysanthemum and gerbera plants in Tuscany (Italy) was examined in four commercial greenhouses. One or two releases at the rate of 2-30 adults/10 m-2 were made. Several sampling methods for estimating leafminer density were used: monitoring adults on sticky yellow cards; systematic counts of empty mines and larvae on leaves and of yielded flowers; isolating the parasitoids and determining the percentage of parasitism. D. isaea occurs naturally with 8 parasitoid species (2 Braconidae, 6 Eulophidae). Sufficient control of leafminers by D. isaea was obtained on condition tht the parasite was released at the rate of 5-30 adults/10 m-2 in newly established glasshouses. In such conditions there was no loss of gerbera flower production in comparison with chemically treated cultivations; nevertheless the problem of secondary pests remains to be solved. On the chrysanthemum, owing to the zero tolerance level for mines, the parasitoid may be used only in the first weeks of crop development since the lower leaves are removed when cutting flowers.