Parasitization of potato tuberworm,Phthorimaea operculella(Zeller), larvae on spring and fall plantings of potato was studied in southern California in 1963, 1964, and again in 1968 and 1969. Foliage mined by larvae was collected at weekly or twice-weekly intervals and held for emergence of adult moths and/or parasites. Thirteen species of parasites were reared, including 7 braconids, 5 ichneumonids, and 1 eulophid. Twelve were indigenous. The remaining species,Orgilus lepidusMuesebeck, was one of 6 parasites imported from Argentina in 1963 and 1964.Agathis gibbosa(Say),Apanteles scutellarisMuesebeck, andChelonus phthorimaeaGahan, were the most common parasites recovered, and in that order. Of 488 and 1,153 host larvae collected in 1968 and 1969, respectively, 57.8 and 53.9% were parasitized. In 1969, 29.4% of the larvae collected from the spring planting were parasitized and 77.4% of those from the fall planting.