A full-fat soybean milk base was produced by grinding blanched soybean cotyledons with water, heating, and homogenizing the resulting durry (Nelson et al., JFS 41(1): 57, 1976). The soy milk base was spray dried using a Necro-Niro portable spray drier. The protein dispersibility index (PDI) of the spraydried powder was altered by changing the processing conditions used during manufacture or spray drying. The PDI of the spray-dried soy milk base was higher when ammonium bicarbonate rather than sodium bicarbonate was used for blanching the cotyledons. The PDI of the spray-dried powder increased when thesoybean durry was homogenized at high pressures and when sodium bisulfite was added to the soy milk base before drying. Sodium bisulfite was the most effective single treatment for increasing PDI. Increasing the pH of the soy milk base to 9 before spray drying increased the PDI of the soy powder. Desludging the soy milk base did not increase the PDI. The best PDI obtained was 72.