Exploratory behaviors as well as pharmacological actions of gamma-aminobutyric acidA (GABAA)/benzodiazepine receptor agonists and inverse agonists were characterized in C57BL/6J and A/J strains of mice. C57BL/6J mice displayed higher levels of exploratory behavior than A/J mice in the light in equilibrium with dark exploration model of anxiety and in an open-field test, suggesting that C57BL/6J mice are less "emotional" and more active than A/J mice, respectively. However, C57BL/6J mice were more sensitive than A/J mice to the anxiolytic effects of diazepam in the light in equilibrium with dark exploration model. In contrast, A/J mice were more sensitive than C57BL/6J mice to the convulsant effects of methyl-beta-carboline-3-carboxylate. C57BL/6J mice showed no evidence of acquisition of a passive avoidance task, while A/J readily acquired this memory task at low levels of footshock. C57BL/6J and A/J mice should be useful parental strains in recombinant inbred lines for investigating the genetic determinants of benzodiazepine-sensitive behaviors and sensitivity to drugs acting on the GABAA/benzodiazepine receptor complex.