Mass production of Schistosoma mansoni cercariae was affected by biological and chemical agents. Rotifers and ostracods, snail predators, were identified in our colony. Rotifers were easily eradicated by washing the aquaria and lettuce with diluted solution of acetic acid. On the other hand, ostracods were difficult to eradicate and led to a high level mortality of infected snails (50-60%). Snails maintained in an incubator at constant temperature and total darkness produced maximum shedding when submitted to brightness and high temperature (about 30 degrees C). The number of cercariae shed was practically the same between pH 5-7. Contaminants such as Cu and Pb added to glass distilled water decreased the cercariae production. In conclusion, laboratory maintenance of large number of infected snails for mass production of cercariae is much simpler and more efficient than the conventional technique with running tap water although a high rate of mortality is observed in the snail colony.