A functional observational battery (FOB) was utilized to assess the effects of 3-day exposure to the formamidine pesticide amitraz in outbred Sprague-Dawley derived and inbred Fischer-344 derived (F344) rats (both from Charles River Laboratories), and in outbred Long-Evans rats obtained from two commercial suppliers (Charles River Breeding Laboratories and Blue Spruce Farms). Significant strain and stock differences were obtained in baseline values for one-third of the FOB measures. Characteristic signs of amitraz exposure consisting of increased excitability, hyperreactivity, and physiological and autonomic changes, were evident in all treated rats. These effects increased with repeated dosing, and many were still present 6 days after dosing. On individual measures, there were differences between the strains and stocks in terms of sensitivity and time course of amitraz effects. In general, Blue Spruce Long-Evans rats displayed more effects of amitraz and F344 rats recovered more quickly than others. On the other hand, Sprague-Dawley rats showed the largest increases in the sensorimotor responses to stimuli.