The tolerance of human subjects to two microfungal food products was studied in separate double-blind cross-over studies. As an addition to the subject's usual diets, cookies with and without 20 g of a product from Fusarium graminearium were fed to a group of 100 individuals daily. In a second study, cupcakes with and without 10 g of Paecilomyces variotii were given daily to 50 individuals. Mild rashes possibly related to one of the microfungal food products occurred in two individuals fed P variotii. Except for a decrease in serum cholesterol during the F graminearium study, no significant changes were noted in 17 serum constituents. During nutritive value studies, digestibility, biological value, and net protein utilization were calculated for the two microfungal proteins and for milk. The values for milk were 95, 85, and 80%, respectively. The values for F graminearium were 78, 84, and 65%, respectively. For P variotii corresponding figures were 81, 67, and 54%. On the basis of these results both microfungal foods may be deemed safe for human consumption at the levels tested.