Egg parasitism ofHeliothis zea(Boddie) and other lepidopterous pests was monitored in a field trial of processing tomato cultivars in 1981 and in several late-season commercial fields of processing tomatoes in the Sacramento Valley of California in 1983, 1985, and 1986. Four species ofTrichogrammawere present:T. pretiosumRiley,T. thalense(Pinto&Oatman),T. deionPinto&Oatman, andT. brevicapillumPinto&Platner. Actual parasitism ofH. zeaeggs exceeded 83% in all fields monitored in 1985 and exceeded 62% in most fields monitored in 1986.Manducaspp. andTrichoplusia ni(Hübner) eggs were also commonly parasitized byTrichogrammaspp. The high levels ofH. zeaegg parasitism recorded in these commercial fields indicates that the current economic threshold, which is based on the abundance of whiteH. zeaeggs, can be increased to account for the mortality caused byTrichogramma. Procedures to incorporateH. zeaegg parasitism into the current integrated pest management program for processing tomatoes are proposed. Acceptable fruit quality at harvest in fields that exceeded the current economic threshold during the growing season provides additional support for increasing the threshold. The effect of insecticide applications onH. zeaegg parasitism is discussed.