Crotoxin is the major component of Crotalus durissus terrificus venom. In view of the presence of high-affinity specific binding sites for crotoxin in the brain, the objective of this work was to investigate whether crotoxin induces behavioral effects in the open-field and hole-board tests. Adult male Wistar rats (180-220 g) treated with crotoxin, 100, 250 and 500 micrograms/kg, ip, administered 2 h before the test, presented statistically significant behavioral alterations (ANOVA for one-way classification complemented with Dunnet test, P < 0.05). In the open-field test, 250 and 500 micrograms/kg of crotoxin increased freezing (from 3.22 sec to 10.75 sec and 11.2 sec) and grooming (from 13.44 sec to 22.75 sec and 21.22 sec) and decreased ambulation (from 64.8 to 39.38 and 45.8). The dose of 500 micrograms/kg also decreased rearing (from 24.9 to 17.5). In the hole-board test, 500 micrograms/kg of crotoxin decreased head-dip count (from 6.33 to 4.00). All the crotoxin-induced behavioral effects were antagonized by an anxiolytic dose of diazepam (1.5 mg/kg, ip. 30 min before the tests). These results show that crotoxin reduced open-field activity and exploratory behavior as well. We suggest that these effects express an increased emotional state induced by this toxin.