Studies were conducted to assess the availability and acceptability of eggs of forest tent caterpillar,Malacosoma disstriaHubner, toTrichogramma minutumRiley for use in inundative releases. Oviposition by the forest tent caterpillar occurred 4–19 July and lasted 7–10 d in southern Ontario. At least 50% of the egg-laying activity occurred during the first 3–4 d. Oviposition was initiated on the same day as female moth emergence, 2 d after male moth emergence. Pheromone traps baited with two-component lures predicted oviposition within 2 d. NoTrichogrammaemerged successfully from 0- to 7-d-old host eggs, although the survival of tent caterpillar embryos exposed at this age to the parasitoids was reduced significantly (from 97.5 to 42.3%). The greatest number ofTrichogrammaemerging from caterpillar egg masses (72.7%)was observed in those eggs exposed to parasitoids 21 d after oviposition, with 43.5 and 12.5% emergence from egg masses exposed at 14 and 28 d after oviposition, respectively. A tent caterpillar egg mass contained 109.8 ± 14.8 (mean ± SE) eggs; parasitoids emerged from 14.4 ± 3.5 of these eggs (13.1% egg parasitism). The number of parasitoids emerging from each parasitized egg ranged from 5.0 to 11.0;69.5% were female and development at 20°C took 14.2 ± 0.2 d. Removal of the spumaline layer from the egg masses increased emergence of parasitoids very slightly. NoTrichogrammasuccessfully overwintered in forest tent caterpillar eggs, although a single dead parasitoid (0.2%)was observed infrequently in eggs simultaneously with a dead pharate larva.Trichogrammapossibly can be used in inundative releases againstM. disstria; however, further studies are needed to determine why the parasitoid kills but does not emerge from tent caterpillar eggs<14 d old.