In this preliminary note on the extent of parasitism of Liriomyza huidobrensis (Blanch.) and Scrobipalpula absoluta (Meyr.) on potato foliage in the Chillon Valley, Peru, the data on the numbers of adult pests and parasites reared from field-collected leaves clearly show that hymenopterous parasites were up to 4 times as abundant in fields that had received no insecticidal treatments whatsoever as they were in fields treated with organic insecticides. An intermediate level of parasitism was recorded from fields in which the only insecticide applied was lead arsenate. The parasites reared from S. absoluta were of the genera Apanteles, Pristomerus, Cremastus and Copidosoma; those from L. huidobrensis were not identified to genus. none