Isolated cockroach ventral nerve cords yield a neuroactive substance following application of either tetra methyl or tetraethyl pyrophosphate. Chromatographically this substance is similar to the toxicant found in the blood of DDT-prostrate cockroaches. On the basis of the similarity of Rf’s, solubility, in activation by alkali, and their reaction to qualitative organic spot tests, the substances produced in vitro by isolated nerve cords when treated with an organophosphate, and and in vivo by DDT-prostration are thought to be identical. A chromatographically similar material was isolated from the blood of DDT-poisoned crayfish. Organic spot tests were positive for nitrogen, and negative for phosphorus. Three tests were for nitrogen, and negative for phosphorus. Three tests were positive for aromatic amines; 2 of these also indicate phenols while 1 indicates aliphatic amines. The results ruled out a pyrrole or derivative, catechold, thioketone or thiol, and also phenol. An ester of acarboxylic acid was indicated by positive results. It is concluded tentatively that the neuroactive substance may be an aromatic amine and an ester.