Abstract Nine chemists in five laboratories collaborated in testing the combined rapid ethyl acetate extraction and sweep co-distillation cleanup method for multiple organophosphate pesticide residues in crops. Pesticides were detected by GLC with the potassium thermionic detector. The six pesticides studied were Diazinon, methyl parathion, malathion, parathion, ethion, and carbophenothion. Six crops—kale, carrots, lettuce, apples, potatoes, and strawberries—were divided into three groups, and each laboratory was selected to work with a specific group. With unknown fortification levels of 1.0 and 0.5 ppm, the collaborators obtained recoveries of 90+% at each level.