As part of a project designed to utilize common dairy waste products profitably, reconstituted dry whey permeate and delactosed whey were tested as growth substrates for mycelia of the edible mushroom Lentinus edodes. This mushroom was chosen because it is possible to profitably cultivate it due to its popular culinary appeal and perceived medical benefits. Growth experiments were performed in petri dishes containing either reconstituted dry whey permeate or delactosed whey as a growth substrate, and the measured response was the size of the growing mycelia colony. When reconstituted dry whey permeate was utilized as a growth substrate, the factors of substrate concentration, pH, and growth temperature were controlled in an effort to determine the optimal growth conditions for the mushroom mycelia. These conditions were determined by applying an analytical method known as response surface methodology (RSM). RSM is a collection of mathematical techniques that is able to determine optimal values for many variables run simultaneously in an experiment. Mycelia were also grown on delactosed whey at different substrate concentrations in an effort to determine if this substrate would be suitable for the growth of mushroom mycelia. Results: RSM was successfully utilized to determine the optimal growth conditions for L. edodes when grown on reconstituted dry whey powder. These conditions were 40 g/L substrate concentration, pH 4 .97, and temperature 23.6°C Delactosed whey was successfully utilized as a growth substrate for L. edodes. However, delactosed whey concentrations above 40% v/v were lethal to the mushroom mycelia, suggesting a possible use for delactosed whey as a fungicide.