To characterize further the behavioral toxicity of amitraz, comparisons were made between the effects of amitraz on motor activity, the acoustic startle response, body temperature, and body weight in male Long-Evans rats. Acute dosage-effect and time-course determinations of motor activity were made using figure-eight mazes. Dosage-effect and time-course determinations for the acoustic startle response were measured using a 13 KHZ, 120 dB(A), 40 ms tone as the eliciting stimulus, at each of three background white-noise levels. Amitraz was administered orally in the vehicle ('Emulphor'+ethanol+saline,d a dosage- and time-dependent decrease in motor activity which lasted from 4 to 96 h post-administration. The effects of amitraz on the acoustic startle response consisted of an increased latency and a decreased amplitude and sensitization. The time-course of effects on the acoustic startle response were more transient (4-24 h) than the effects on motor activity. Amitraz-exposed animals had decreased body weight that did not return to control levels until 120 h (five days) post-administration. (Copyright (c) 1989 Society of Chemical Industry.)