Poly(DL-lactide-co-glycolide) (PLGA)/polyethylene glycol (PEG) microspheres are one modality of controlled delivery of biologically active molecules that would further the development of engineered tissues. As a possible mechanism to stimulate angiogenesis within an engineered tissue, vascular endothelial growth factor (VEGF) and bovine serum albumin (BSA) were coencapsulated into microspheres fabricated from PEG and 50/50 PLGA using a solid-encapsulation/single-emulsion/solvent extraction technique. Two VEGF/BSA ratios were studied: 1:2000 and 1: 10,000 Analysis consisted of the loading efficiency, particle size distribution, bright-field microscopy, scanning electron microscopy, release kinetics, and an in vitro human umbilical vein endothelial cell proliferation assay to assess biological activity of the released VEGF. Results show the microspheres could be manufactured, stored, and degraded over 28 days. The burst release rates for 1:2000 and 1:10,000 VEGF/BSA microspheres were 71.87 ± 8.11 and 27.91 ± 1.71 ng/mL (mean ± standard error of the mean), respectively; steady-state release rates were 6.56 ± 1.10 and 2.21 ± 0.47 ng/mL, respectively. The microsphezes released biologically active VEGF, and the VEGF increased the proliferation of HUVECs in culture (p <. 05). The successful development of a novel, cost-effective, scalable technique for producing microspheres loaded with biologically active proteins is presented. Using the data obtained from these studies a defined concentration of microspheres will deliver a quantifiable level of VEGF at a known release rate. © 2000 John Wiley and Sons, Inc.