A continuing study of Catharanthus lanceus alkaloid fractions, in a search for new antineoplastic alkaloids, has led to the isolation of Catharine, a dimeric indole alkaloid found previously only in the related C. roseus. A continued investigation of alkaloid fractions obtained from C. lanceus has resulted in the isolation of a second dimeric alkaloid, Catharine, from this plant. High resolution mass spectrometric measurements have shown that Catharine has the formula C₄₆H₅₄N₄O₁₀ and is made up of a vindoline moiety and an alkaloid moiety with a molecular formula of C₂₁H₂₃N₂O₄. The isolation, characterization, and partial structure elucidation of this alkaloid is reported here.