In general in any fermentation the volume of wastewater is too high. The excess water might be utilized to reduce consumption of process water. In this investigation cell-free culture filtrate was used instead of process water. In batch experiments, cell-free culture filtrate was used in ratios between 0·1 and 1·0 for eight subsequent batches. The specific growth rate was higher than that of the first batch for reusability ratios between 0·1 and 0·8 in all batches. Synthesis of penicillin amidase was found to be more suitable in the fourth batch with a recycle ratio between 0·6 and 1·0. An extracellular protein factor was found to influence the synthesis of penicillin amidase. © 1991.