The potency and efficacy of the selective dopamine D2 receptor agonist quinpirole, the mixed D1/D2 agonist apomorphine, and the selective D1 receptor agonist SKF 38393 in producing hypothermia and changes in locomotor activity were evaluated in four strains of mice: CBA/J, C57BL/6J, ICR Swiss and CF1. CBA/J mice previously have been shown to be deficient in dopamine cell and receptor number relative to other strains such as C57BL/6J mice, whereas ICR Swiss and CF1 are commonly used strains of mice. Quinpirole (0.125 to 1.0 mg/kg) was equiefficacious and equipotent in producing hypothermia in all 4 strains. Apomorphine (0.125 to 16 mg/kg) was equiefficacious in producing hypothermia in all 4 strains, but was approximately four-fold less potent in CBA/J mice than in the other strains. SKF 38393 had little effect on body temperature in any of the 4 strains. Basal motor activity was lowest in CBA/J mice, and tended to be highest in ICR Swiss mice. Quinpirole (0.125 to 32 mg/kg) had no effect on motor activity in CBA/J mice, but decreased motor activity in the other 3 strains. Apomorphine (1 to 16 mg/kg) produced modest increases in motor activity in all 4 strains. The magnitude of the changes produced by apomorphine was comparable in all strains when expressed as change from mean control values. SKF 38393 (8 to 64 mg/kg) also increased motor activity in all 4 strains, with comparable increases when expressed as change from mean control values. The present results are consistent with the interpretation that inherited deficiencies in dopamine cell and receptor number in CBA/J mice produce functional decrements in D2, but not D1, dopamine receptor function.