The kinetics of gibberellic acid (GA(3)) production and growth of Gibberella fujikuroi was studied in a batch cultivation process at pH 5.0 and temperature 30degreesC. It features 12 g/l accumulation of biomass in the initial 50 It of fermentation followed by GA(3) production of 1 g/l during 50-170h. The effect of initial C/N ratio on maximum specific growth rate (mu(max)) was studied in the range 7.97-796.8. Increasing carbon supply and therefore increasing C/N ratio was found to both limit and inhibit the growth of culture. Maximum specific growth rate (0.096 h(-1)) was observed at C/N ratio of 119.5 and no growth (mu = 0) was observed at C/N ratio of 917.8. An unstructured mathematical model was proposed to describe the batch kinetics of fermentation. The model parameters were evaluated using the actual batch cultivation data. The proposed model described well the observed experimental kinetics with respect to substrate, biomass and product formation. The model will facilitate further optimization studies of GA(3) production. (C) 2004 Elsevier Inc. All rights reserved.