The authors describe continuous cultivations of Escherichia coli possessing high penicillin-acylase activity in corn-steep liquor, peptone, and ammonium phenylacetate containing nutrient medium. If the cultivation is performed in the absence of ammonium phenylacetate the enzymic activities of cells from the batch as well as the continuous cultures are very low. The enzymic activity of cells in the batch process was considerably increased by the addition of 0.01570 ammonium phenylacetate to the nutrient medium. Further increase of ammonium phenylacetate concentration did not result in any further increase of acylase activity. Continuous cultivation of the bacteria a t the above ammonium phenylacetate concentration was unsuccessful, as the enzymic activity of the bacteria constantly decreased during the process. On increasing the concentration of ammonium phenylacetate in the medium to 0.15% the authors succeeded in maintaining the enzymic activity of the bacteria at the same level as in the batch process performed at 0.015'% concentration, throughout the whole continuous cultivation. At the dilution rate D = 0.5 hr.-I the concentration of cells in the culture effluent from the fermentor a t the steady state was equal to cell concentration a t the end of batch cultivation. In relation to the cultivation time the output of cells in continuous cultivation is almost seven times higher as compared with the batch process.