Administration of diazepam was suggested to exert immuno-suppressive properties in mice. In the present study, we explored the time and dose-dependence of diazepam effects on delayed hypersensitivity to sheep erythrocytes in Balb/c mice. DTH response was only depressed when diazepam was injected shortly after immunization and this effect on DTH induction was found with doses of 4 and 8 mg/kg ip while lower doses (0, 5, 1 and 2 mg/kg) remained ineffective.