Adult Schistosoma bovis worms survived in a defined medium up to 18 days; but the female worms produced no ova in such medium. Addition of horse serum to the defined medium increased the period of survival to a maximum of 24 days. During this period the adult female worms remained in copula and continued to produce non-viable ova up to the end of the third week. During the major portion of their survival period, worms in both media showed active somantic movements with frequent contortions and body flexing. Gut action was rapid and almost continous.