Batch fermentations were used to study the effect of different glycerol concentrations and pH conditions on growth of recombinant Pichia pastoris. Two strains of P. pastoris were used: a wild-type in methanol utilization (Mut(+)) and a mutant defective in methanol utilization (Mut(-)). Under constant pH conditions of 5.0, glycerol concentrations up to 12% were efficiently utilized. Cell yield (Y-x/s) of about 0.8 and a final cell density of about 95 g/L (dry cell) were achieved. However, there were significant differences (probability [Pr] > F 0.0351) in specific growth rates between the initial glycerol concentrations of 2, 7, and 12%. When fermentations were conducted without pH control, growth continued until the pH had decreased to about 2.5. Growth stopped at pH 2.2 with uncontrolled pH, and residual glycerol concentrations were greater than 2%. As a result, Y-x/s decreased to about 0.3. There were no differences between Mut(+) and Mut(-) strains during cell growth on glycerol.