A red pigment extracted from male gemetophytes of Equisetum arvense and E. hyemale and from young vegetative stems of E. arvense and overwintering stems of E. kyemale was identified as a carotenoid similar to but mot identical with rhodoxanthin. Its specific occurrence in the gametophyte generation accompanying antheridial formation suggests a relationship between carotenoids and reproduction, a relationship also apparent in other groups of organisms but not yet elucidated.