Croton ruizianus Muell.-Arg. (Euphorbiaceae) is a small shrub growing in the Central sierra of Peru. The infusion of its leaves is employed in traditional Peruvian medicine as a vulnerary and an antispasmodic. To date, species of Croton have yielded alkaloids of the aporphine, proaporphine and morphinandienone groups and N-methyltyramine derivatives. For this reason we have now investigated the alkaloid fraction from the leaves of C. ruizianus. C. ruizianus leaves were collected in June 1993 in Aija Province, Ancash Department, Peru. The air-dried and powdered leaves (500 g) were extracted in a Soxhlet for 48 h with MeOH. The extract was concentrated in vacuo and the residue was dissolved with ethyl acetate and acidified with a solution of tartaric acid (4%). The water phase was alkalinized to pH 9.0 and extracted with CH2CI2. The alkaloid fraction was chromatographed on a silica-gel column and purified by RP-HPLC. Crotsparine (14.2 mg) and jacularine (12.1 mg) were recovered and their structures were determined by comparing their ¹H and ¹³C NMR data with those reported in the literature. The alkaloids isolated from C. ruizianus belong to the proaporphinic group. This study confirms the presence of crotsparine and jacularine in the genus Croton and can be useful in its chemical characterization.