A bioassay for detection and determination of minute quantities of carbamate insecticides in fruit and vegetable crops was developed with Daphnia magna Straus. The Daphnia bioassay was quick, simple to prepare, reproducible, and proved more sensitive to carbamates than that for Drosophila melanogaster Meigen. Crops were treated in the laboratory and then extracted by a modification of an established method. The extracts of unknowns were evaporated, reconstituted with dimethvl sulfoxide, and injected in 0.025-ml quamities into 13×100 mm test tubes containing 2.5 ml of water. D. magna specimens were introduced, and toxicity observations were taken after 30 minutes. A standard curve was prepared daily in reagent grade solvents; check crop extractions were seldom necessary. Recoveries between 85-100% were consistently obtained.