A Functional observational battery (FOB) was utilized to provide a semiquantitative description of the hyperreactivity, excitability, and debilitation produced by amitraz. Adult male Long-Evans rats were administered either vehicle or 10, 25, 50, 100, or 200 mg/kg amitraz ip. They were tested with the FOB immediately before dosing, at 1 and 4 hr, and at 1, 2, 4, and 8 days after dosing. Higher doses (100-200 mg/kg) produced increased reactivity to manipulation, tenseness, and aggression. Most or all doses produced depressed arousal and rearing activity, hypothermia, body weight loss, and autonomic changes including ptosis, chromodacryorrhea resulting in facial crustiness, loss of the pupil reflex, and decreased defecation. Altered gait and decreased landing foot splay were also produced by amitraz. For the most part, effects of lower doses (10-50 mg/kg) were reversible by 2 to 4 days after treatment. In the higher dose groups, however, signs of toxicity were evident, and in some cases even more prominent (e.g., handling hyperreactivity), 8 days after a single dose of amitraz. The FOB thus provided a semiquantitative description of the magnitude and time course of many features of the amitraz toxicity syndrome.