Three alkaloids of the stem bark of Strychnos dolichothyrsa Gilg ex Onochie et Hepper (Loganiaceae) were isolated and identified as caracurine V and its mono- and di-N-oxide by comparison with synthesized compounds. 13C-NMR was used to confirm the structure of the N-oxides. The muscle relaxant activity and the toxicity of the N-oxides were less than those of caracurine V.