Triadimefon is an agriculturally important triazole fungicide. Experiments were conducted to characterize the behavioral toxicity of triadimefon using a measure of motor activity. Male Long Evans hooded rats, approximately 70 days old, received triadimefon po in 2.0 ml/kg corn oil. Motor activity testing was conducted for 1 hr in figure-eight mazes. For the dosage-effect determination triadimefon (50-400 mg/kg) was administered 1 hr prior to testing. In the time-course study, triadimefon (200 mg/kg) was administered either 0.5, 1, 2, 4, 8, or 24 hr prior to testing. In the repeated dosing experiment animals received triadimefon (100 mg/kg) daily for seven days and were tested 24 hr after the last exposure. Triadimefon produced significant hyperactivity following dosages of 100 and 200 mg/kg. The hyperactivity was rapid in both onset (0.5 hr) and recovery (8.0 hr). Repeated dosing with 100 mg/kg/day revealed no cumulative effects nor tolerance. The results indicate that triadimefon produces a transient hyperactivity at dosages 17 to 33% of the reported LD50. (Copyright (c) 1988 by The Society of Toxicology.)