Five occupants of an office developed symptoms compatible with organophosphate intoxication after application of chlorpyrifos, a moderately toxic pesticide. Recovery of erythrocyte cholinesterase levels occurred during the subsequent three months but followed an exponential distribution rather than the constant rate of recovery most investigators have assumed. This pattern suggests redistribution of the active organophosphate after absorption to a second body compartment with subsequent slow release of the still active substance into the bloodstream.