Industrial Crops and Products j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / i n d c r o p Antiproliferative activity and constituents of leaf extracts of Croton sphaerogynus Baill. (Euphorbiaceae) a b s t r a c t Several Croton species have been used in traditional medicine and contain substances active against cancer, such as diterpenoids and alkaloids. Croton sphaerogynus is a shrub from the Atlantic Rain For-est in southeastern Brazil. The main goal of this study was to characterize the main constituents of the leaf extracts of C. sphaerogynus and evaluate their in vitro antiproliferative activity against tumor cell lines. Hexane, dichloromethane and methanol extracts of leaves were analyzed by GC/MS and eval-uated for their in vitro antiproliferative activity on the cell lines 786-0 (kidney), HT-29 (colon), K562 (leukemia), NCI-ADR/RES (drug resistant ovary), NCI-H460 (lung), MCF-7 (mammary), PC-3 (prostate), OVCAR-3 (ovary), U251 (glioma) and UACC-62 (melanoma). Relevant constituents in dichloromethane and hexane extracts were abietane, podocarpane and clerodane type furano diterpenes. Dicloromethane and hexane extracts exhibited activity against NCI-H460 (GI 50 0.26 g/mL and 0.33 g/mL, respectively) and K562 (GI 50 0.60 g/mL and <0.25 g/mL, respectively). Taking into account all cell lines tested, the dichloromethane extract was shown to have higher activity (mean log GI 50 0.86) than hexane and methanol extracts (mean log GI 50 1.26 and 1.49, respectively). The antiproliferative activity observed in the present work is probably accounted for by the abietane and/or podocarpane diterpenes.