Functional observational battery suggested by EPA, was applied to neurotoxicity screening studies. In previous experiments an organophosphorous pesticide, chlorfenvinphos (CVP), was used. It was administered intraperitoneally to male rats at the doses of 1, 3, 6 mg/kg of body weight; edible oil was administered to the control group. Tests were performed 3 hrs, 24 hrs and 7 days after the administration of the these substances. The set of tests concerned motor, sensory and vegetative functions. The influence of the dose of 6 mg/kg on rats was particularly evident. A number of disorders, like tremor, hypersalivation, dysbasia and hypotaxia, not observed in animals to which lower doses of CVP had been administered, were noticed. The mortality rate in this group was 25%. Earlier studies revealed neurotoxicity of CVP administered at the dose of 3 mg/kg, which when compared to the present results of the experiment indicates low sensitivity of this battery of tests taken as a whole. The disadvantage of the battery lies also in applying the quality evaluation scale in many cases, which makes carrying out statistical analysis difficult. Behaviours not formulated in this scale were observed. The observation of animal locomotor activity proved to be the most reliable and objective neurotoxicity evaluation index both in the previous and present studies.