A routine to maintain infected snails Biomphalaria glabrata able to produce 1-2 million cercariae per week and a mean shedding of about 3,500 cercariae per snail was quantitatively described. To a monthly production of about 5.3 and 6.5 million cercariae during the years of 1982 and 1983 it was necessary to expose an average of 1,557 and 1,957 snails, respectively. The efficiency described was maintained by infecting 2,000 snails per month (infectivity index of about 60%). A maximal production of 6,000 cercariae/snail was obtained in the period between 56-70 days after the snail infection by miracidia. By this period, however, 90% of the infected snails were dead. In the summer of 1982-1983 it was observed an impairment on the daily cercarial harvests which was related to ambient temperature increase, and the presence of rotifers in the aquaria water. When the cercariae were transformed into schistosomula in vitro, a yield of 55% schistosomula was obtained, with 7% of tail contamination. Lyophilization of cercariae produced 50.9 ± 63 g dry weight per 1,000 cercariae.