Experiments to evaluate the residual contact toxicity of five carbamates to adult Anopheles stephensi have shown that four of the compounds (Hercules 7522, UC 10854, Bayer 39007 and RE-5305) were effective as contact insecticides for at least three months when applied as wettable powders on plywood at a dosage of 1 g/m(2). They were rapidly sorbed, however, on dried mud bricks stored at 25 degrees C and 50%-55% relative humidity, and were unstable on fresh limewash. The authors conclude that, although these compounds show promise as residual insecticides, their residual properties may be expected to vary according to the properties of the building materials to which they are applied. A fifth carbamate, Sevin, was much less effective as a contact insecticide.