In a continuing effort to study thoroughly the alkaloids of Catharanthus roseus, new dimeric alkaloids were isolated and characterized. Structures are proposed for leurocolombine and vinamidine based on UV, IR, PMR, high-resolution mass spectrometry, and CMR. Pseudovincaleukoblastine diol was identified by PMR and mass spectrometry. Leurocolombine exhibited antimitotic activity and marginal antitumor activity against the Ridgeway osteogenic sarcoma.