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A novel combination of extraction and detection methods is demonstrated for pesticide residue analysis in vegetable samples. Acetylcholinesterase (AChE) inhibition was used as a simple colorimetric test for organophosphates/carbamates (OP/C), and was tested with extracts from the widely-used QuEChERS extraction method. In the absence of pesticide, diluted (50% with water) acetonitrile did not inhibit enzyme activity, demonstrating the compatibility of this extraction solvent with the AChE inhibition test. QuEChERS extraction of chlorpyrifos-spiked tomato, spinach and lettuce samples indicated a high sensitivity to OP/C, with AChE inhibition occurring in the ppb range. The applicability of this method combination was tested by screening tomatoes from 18 different sources, including private gardens, farmer’s market venders, and local supermarkets. Tomatoes from one private garden, three “certified naturally grown” farmer’s market venders and two “organic” supermarket source had AChE inhibition significantly above nominally pesticide-free controls, suggesting the presence of OP/C residue. These residues were likely below levels of health concern, as indicated by lack of complete AChE inhibition, and the absence of inhibition upon sample dilution. This study demonstrates that the combination of QuEChERS extraction and AChE-inhibition detection provides a relatively simple and inexpensive alternative for detection of OP/C in vegetable samples.