The cytotoxic effects on HCT 116, Hep G2 and HCT 116/VCR 100-1-1 cell lines of synthetic 4'-O-alkylaloenins (2-17), 4'-O-benzylaloenin (18) and 4'-O-allylaloenin (19) were examined by MTT assay, and compared with that of aloenin (1) isolated from Aloe arborescens Mill. Var. natalensis Berger which