To investigate the contribution of the PKCγ isoform of protein kinase C (PKC) in neurochemical pathways regulating anxiety, mice lacking the gene encoding PKCγ were tested with heterozygote and wild-type littermates in three approach-avoidance tests of anxiety. Null mutant mice consistently displayed a decrease in baseline anxiety-related behaviors in the elevated plus-maze, the black/white box, and the mirrored chamber. In the elevated plus-maze, mutant mice entered the open arms significantly more often and spent more time in the open arms of the maze. In the black/white box, transitions between the compartments were greatest in the null mutant mice, and in the mirrored chamber, mutant mice were markedly less anxious with significantly decreased latencies to enter and more time spent in the chamber. Indices of locomotor activity in the mazes and tests of activity in home cages indicated that the reduced anxiety observed in the mutant mice was not due to baseline locomotor activity differences among the genotypes. These results suggest that PKCγ be considered as one factor in the etiology of anxiety, perhaps via its post-synaptic regulation of GABA_A and 5-HT₂ receptors, two receptors implicated in the neurobiology of anxiety.