In Biomphalaria glabrata parasitized by Schistosoma mansoni there was an increase in relative weight of the digestive gland-gonad complex and a decrease in glycogen in that complex and in the remainder of the carcass by day 25. Glycogen levels further decreased close to zero and remained at this low level for the duration of the experiment. Relative weight of the digestive gland-gonad reached a peak at day 30 and decreased toward normal by day 40. Galactogen levels in the albumen gland, although decreased slightly, were not significantly lower than in normal snails. In starved snails, glycogen and galactogen decreased significantly below normal at day 21 and remained at a low level until the experiment ended. This study raises the possibility that starvation of the host by the parasite may play a significant role in the pathology observed in this infection.