Low brain and serum cholinesterase activity were found in several species of wading birds. The area from which these birds were taken recently had been sprayed with the organophosphorous insecticide fenthion (O, O-dimethyl O - [4-(methylthio)-m - tolyl] phosphorothioate). Analysis of stomach contents and water samples revealed residues of fenthion. These findings suggest that fenthion caused lethal cholinesterase depression.
