The recoveries of genetically engineered human growth hormone (hGH), carboxypeptidase and -galactosidase, fromE. coli broths have been studied, using the process of microfiltration. The suspension superficial velocity was found to significantly influence the yields obtained. However, the molecular weight of the product could be an important factor in microfiltration. Simple washing procedures seem to be adequate for effective rejuvenation of the membrane.