This paper compares the anxiolytic-like actions of toluene in two anxiety paradigms, the burying behavior and plus-maze tests, in 5-HT(1B) knockout (KO) and 129/Sv-ter wild-type (WT) mice. Static exposures were conducted in 29-l gas chromatographic jars. Animals were exposed to toluene (0, 1000, 2000 or 4000 ppm; n=8-12, each) for 30 min, and immediately after, tested in one of the anxiety paradigms. Motor coordination was evaluated in the rota-rod test in independent groups of mice. Toluene produced a dose-dependent decrease in anxiety-like levels in both anxiety paradigms and in both the strains. However, toluene exerted its effects at lower concentrations in KO mice than in the WT strain. These results cannot be attributed to a decrease in motor coordination since all the animals behaved similarly in the rota-rod test, regardless of the treatment. To discard any inherent difference in the nociception threshold between strains, mice were tested in the hot plate immediately after being exposed to either air or toluene. Toluene increased nociception in a similar fashion in both the strains. Our results suggest that 5-HT(1B) KO mice are more sensitive to those of toluene's actions related to anxiety, but not to those related with motor coordination or nociception. Data are discussed in terms of toluene's mechanisms of action and on differences between WT and KO animals.