The kinetics of the production of gibberellic acid (GA3) in conventional batch culture was compared with that obtained in fed-batch cultures at three different feeding regimes with media containing protein N, one of which was calculated to maintain a constant biomass, and two others able to promote linear growth. It was found that the production of GA3 improves substantially in the latter two cases, and that the general model applicable to the formation of a secondary metabolite correctly predicts the results if one dispenses with the assumption of avoiding the increase in the biomass during the production phase.