An empirical kinetic model is proposed for the batch production of poly(glutamic acid) from Bacillus subtilis IFO 3335. In addition, the proposed model was used to fit the kinetic data of poly(glutamic acid) production from other bacterial strains using different media, as well as kinetic data from different strains for the production of the exocellular biopolymers dextran, hyaluronic acid, xanthan, alginate, and the endocellular biopolymer polyhydroxybutyrate. The empirical model treats the biopolymer as a component of the biomass and fits the experimental biomass data using a sigmoidal relationship that includes the maximum specific growth rate, mumax, and the substrate saturation parameter, K-S. An empirical parameter, the relative coefficient (r), quantifies, in relative terms, the degree of nongrowth-associated biopolymer formation. (C) 2004 Wiley Periodicals, Inc.