The influence of the host immunosuppression on antimycobacterial effects of isoniazid, rifampicin or streptomycin was studied on animal models. Differences in survival rates of mice influenced or uninfluenced by azathioprine (Imuran) and exposed to six applications of antituberculous drugs (given once a day in the monotherapy) were statistically evaluated. The dose-dependent antimycobacterial effects of rifampicin or isoniazid were not significantly altered by the immunosuppression of the host. In contrary to that definite dose-dependent effect of streptomycin, observed in azathioprine-uninfluenced mice, cannot be confirmed in immunosuppressed mice in which no effect of streptomycin on the survival of tuberculous mice could be estimated.