BACKGROUND: The poly(3-hydroxybutyrate)P(3HB)is a polyester synthesized by many bacteria and stored as an energy reserve material in the cell cytoplasm as water-insoluble inclusions. The aim of this research was to present a mathematical modeling approach in order to describe the culture kinetics of the bacterium Bacillus megaterium for the production of poly(3-hydroxybutyrate). RESULTS: Four different models were proposed, differing in the expressions used for specific growth and polymer production rates. The predictions of these models were compared with experimental data and against the results of other models reported in the literature. CONCLUSION: Analysis of the experimental data under controlled and uncontrolled pH conditions showed that the inclusion of a correction factor for products formation, as well as a term related to the influence of H+ cations, are important for the correct modeling of this bioprocess. Compared with earlier models reported in the literature the proposed models show better fitting, with less or equal numbers of parameters, and provide parameter estimates with much lower variability. (C) 2011 Society of Chemical Industry