From 1959 through 1964, Federal and State entomologists in Idaho, Oregon, and Washington imported, reared, and releasedPraon pequodorumViereck,Aphidius ervi pulcherBaker,Aphidius ervi erviHaliday, andAphidius smithiSharma&Subba Rao to augment present populations or to replace lost populations of native parasites capable of providing biological control of the pea aphid,Acyrthosiphon pisum(Harris), on peas and alfalfa. As a result, populations of P.pequodorumandA. pulcherhave become increasingly effective against this pest, andA. ervihas become established in coastal Oregon and probably throughout Washington and Idaho. Also, in only 5 years,A. smithihas spread into nearly all the alfalfa- and pea-growing areas of the Pacific Northwest.