A procedure is described which is applicable to the screening of large numbers of samples for anitcholinesterase activity. The method is sufficiently sensitive to detect cholinesterase depression due to as little as 30 ppt paraoxon; 3 ppb malaoxon or 2 ppm of carbaryl in either ethylene glocol or water. While the method does not allow the absolute differentiation between compounds which might be present, some classification is possible, i.e., for compounds which must be activated before they possess anitcholinesterase activity. The technique can be made more specific through manipulations of types of cholinesterase used and substrates employed. The major usefulness of the technique at this time is for screening.