A mathematical model was developed to predict the growth kinetics of a pure culture of Zoogloea ramigera (NRRL 3691) under carbon-, oxygen-, and nitrogen-limited conditions at variable medium pH values and agitation rates. Experimental results were obtained in a continuous fermenter at steady state and processed with nonlinear regression to yield the best fit multieffect expression. A multisubstrate model was constructed by nonlinear analysis of various single substrate kinetic expressions in different combinations. The pH and agitation effects were expressed as multipliers on the multisubstrate model. The model represented the growth of microorganism fairly well for variable pH and agitation values under simultaneous carbon, oxygen, and nitrogen limitations.