A study was carried out to determine if snail nutrition influences infectivity of Schistosoma mansoni cercariae for mice. The percentage of worms recovered after infection was the chief criterion used to determine infectivity. Six groups of Biomphalaria glabrata were raised on separate diets of (1) a standard formula with and without lettuce, (2) ‘Gaines Meal’ dog food (compressed pellets), (3) a commercial chicken feed, (4) Romaine lettuce, (5) squash, and (6) the rhizome of a Caladium plant. At 6 weeks the snails were infected and the cercariae resulting from the different snail infections were used to infect mice. Seven weeks later the mice were sacrificed and worms were recovered by perfusion. Snails raised on squash, lettuce and the Caladium rhizome were only one-half the size of those receiving either the standard formula or the ‘Gaines Meal’ at the time of infection, and produced fewer than one-fifth as many egg clutches. However, the percentage parasitemia on all six groups of mice only varied from 49 to 55%, and there were no apparent differences in the size or development of the worms from the different groups of mice.