The in vivo application of angiogenic growth factors such as endothelial cell growth factor (ECGF) is limited due to the short half-lives (minutes to hours) as well as the non-localized, nonspecific delivery by conventional methods. Previously, we studied the short-term release characteristics of ECGF immobilized within an alginate microbead release system. In the present study, we determined the long-term release profile of ECGF from the same system, and also evaluated whether physical (shape) modification of the delivery system (i.e. calcium alginate-immobilized ECGF) affected the rates of ECGF release. Finally, we examined the controlled release of ECGF in vivo. ECGF was immobilized in calcium alginate and prepared as either: (i) microbeads, (ii) a continuos long filament shape, or (iii) a 2-dimensional, flat sheet configuration. The different configurations of alginate-immobilized ECGF were separately incubated for 4 periods of 2 weeks each. ECGF release was determined spectrophotometrically. The most substantial release occurred within the first 2 weeks (64% released), with each subsequent period releasing decreasing amounts (16% at 4 weeks, 12% at 6 weeks, 6% at 8 weeks). The physical shape of the ECGF delivery systems did not produce a significant effect on the overall ECGF release profile. Viable ECGF release from the calcium alginate delivery systems occurs for approximately 8 weeks in vitro. Our preliminary in vivo studies showed enhanced angiogenesis following transplantation of alginate-immobilized ECGF versus alginate without ECGF. We conclude that calcium alginate-immobilized ECGF delivery systems protect and prolong the delivery of angiogenic growth factors and have important implications in wound healing, surgical reconstruction, and cell transplantation (tissue engineering) studies.