Concentration:response regressions were established for male and female Panonychus ulmi from dicofol resistant and susceptible laboratory colonies using a rapid assay technique which utilizes pesticide residues in enclosed Petri dishes. Modification of the technique, which was developed for females, allowed reproducible results with males. Males and females from the resistant population showed similar levels of resistance compared with the susceptible population (ca. 4-fold). Within populations, males were approximately 3-fold more sensitive than females. Implications of these differences for field populations and the usefulness of males in inheritance studies are discussed.