Leishmanicidal activity of 24 derivatives of naturally occurring and abundant triterpenes belonging to the lupane series, betulin, betulinic acid and betulonic acid, is described in this study. The easily modified positions of the lupane skeleton, the hydroxy groups of C-3 and C-28, as well as the carbon-carbon double bond C-20-C-29 were used as a starting point to prepare a library of triterpenoid derivatives for bioactivity studies. The compounds were evaluated against Leishmania donovani axenic amastigotes on a microplate assay at 50 microM. GI(50) values of the most effective compounds were evaluated, as well as their cytotoxicity on the human macrophage cell line THP-1, and anti-leishmanial activity against L. donovani-infected THP-1 macrophages was determined. Betulonic acid was the most potent derivative, yielding a GI(50) value of 14.6 microM. Promising and distinct structure-activity relationships were observed, and these compounds can be regarded as significant lead molecules for further improvement and optimization.