Alopecuridine, an alkaloid from Lycopodium alopecuroides L., is shown to be 4α-hydroxyfawcettimine 1. Calcium-ammonia reduction of alopecuridine 1 followed by acetylation gives N-acetylfawcettimine (5). A single crystal X-ray crystallographic analysis defines the complete structure and stereochemistry of N-acetylalopecuridine. © 1974.