Pretreatment of mice with hot water and alkaline extracts of Catuaba casca (Erythroxylum catuaba Arr. Cam.) effectively protected them from lethal infection of Escherichia coli and Staphylococcus aureus. The extracts significantly inhibited both the human immunodeficiency virus (HIV)-induced cytopathic effect and the expression of HIV antigen in HIV-1HTLV-IIIB or HIV-2ROD infected human lymphotropic virus type I (HTLV-1) positive MT-4 cells. The 50% effective concentrations of the active fractions (21-263 micrograms/ml) were 1/4 - 1/43 of their 50% cytotoxic concentrations. Their anti-HIV activity was shown to be induced, at least in part, via the inhibition of HIV adsorption to the cells. The data suggest a medicinal potential of Catuaba extracts against opportunistic infection in HIV patients.