A technique for ensuring the controlled release of microgram and smaller amounts of biologically active epidermal growth factor (EGF) from polymeric delivery systems is described. We show that albumin in milligram quantities can facilitate the sustained release of picogram amounts of EGF for at least 3 wk. The EGF-containing polymer matrix can be placed directly into cell culture and will increase the proliferation rate of serum-starved cells. The method reported here should be suited particularly to the delivery of biologically active growth factors that are obtainable in only microgram or smaller amounts.