The formamidines are a relatively new class of pesticides which are effective against mites, ticks, and other insects. Chlordimeform, a representative of this class, is of great toxicological interest because it is effective against pests which are resistant to organophosphate and carbamate pesticides. Likewise in birds and mammals, chlordimeform produces symptoms of toxicity which are different from those produced by organophosphate and carbamate pesticides. In terms of biochemical effects, chlordimeform has been shown to inhibit monoamine oxidase which increases brain levels of norepinephrine and serotonin. This effect has been interpreted as the action by which chlordimeform produces the symptoms characteristic of the 'serotonergic syndrome', a behavioral pattern consisting of forepaw treading, head weaving, hind limb abduction, rigidity, Straub tail, and tremor. However, other biochemical effects of chlordimeform have also been noted. Chlordimeform has actions similar to local anesthetic agents; it inhibits prostagland in sysnthesis, and in the firefly, is an agonist at octopamine receptors. Because of the paucity of studies on the behavioral effects of chlordimeform, and the diversity of biochemical effects reported, the present studies were initiated. The pigeon was selected for experimental study because of the extensive use of the pigeon in characterizing the behavioral effects of drugs and toxicants affecting the central nervous system and the need for a comparative neurotoxicology in the assessment of a pesticide's impact on the environment.