AbstractBatch experiments were run using heterogeneous populations to determine whether a hyperbolic equation of the type suggested by Monod could be used to depict the relation between specific growth rate, μ, and NH3‐N concentration when ammonia N was the growth‐limiting nutrient. The heterogeneous populations employed were developed from sewage seed grown on glucose at various levels of nitrogen and various dilution rates in completely mixed continuous flow reactors. It was found that the hyperbolic function could be used. Values of μmin the range of 0.4–0.7 hr−1were observed, and values ofKs, in general, ranged from 1.5 to 4.0 mg/l. Variation in the values of these growth “constants” did not follow any discernible pattern related to past growth history (i.e., COD:N ratio or dilution rate at which the cells were prev