A collaborative study, sponsored by the International Program on Chemical Safety, examined the intralaboratory and interlaboratory reliability of a functional observational battery (FOB) and an automated motor activity assessment in eight laboratories worldwide. In the first study, rats received chlorpromazine (50533) doses up to 4mg/kg or triadimefon (43121433) doses up to 300mg/kg and motor activity counts were determined. In the second study, rats received a p,p'-DDT (50293) dose of 75mg/kg, varying doses of parathion (56382), or short term, repeated acrylamide (79061) doses of 40mg/kg per day. The FOB was performed 6 hours after p,p'-DDT exposure, at varying times following parathion exposure, and one to three days following acrylamide exposure. In the first study, all laboratories reported significant, dose dependent decreases in motor activity with chlorpromazine exposure. All laboratories reported decreases of at least 40%. Although most laboratories reported significant, dose dependent increases in motor activity with triadimefon exposure, the magnitude of the activity increases varied considerably among the laboratories. In the second study, most laboratories observed gait changes, increased foot splay, decreased hindlimb grip strength, and decreased body weight with acrylamide exposure. The magnitude of the effects of acrylamide exposure varied considerably among the laboratories. Nearly all laboratories observed significant gait changes, tremors and/or myoclonus, increased click response, and increased body temperature with p,p'- DDT exposure. Although most laboratories observed salivation, tremors and/or mouth smacking, miosis, gait changes, decreased arousal, decreased tail pinch response, and decreased body temperature with parathion exposure, the magnitude of the effects varied substantially among the laboratories. The authors conclude that differences among laboratories are attributable to miscommunications, protocol difficulties, and dose limitations. All laboratories meet the criteria established by the IPCS collaborative study steering committee.