Controlled release of basic fibroblast growth factor (bFGF) from gelatin microspheres achieved de novo adipogenesis at the implanted site of a basement membrane extract (Matrigel). Following subcutaneous co-implantation of Matrigel and gelatin microspheres incorporating 0.1 mug of bFGF into the back of mice, adipose tissue was formed at the implanted site after 4 weeks postoperatively although the extent increased with implantation time. Formation of adipose tissue was significantly faster than the co-implantation of Matrigel, and 0.1 mug of free bFGF while a larger volume of the adipose tissue formed was retained 15 weeks later. When measured in Matrigel co-implanted with the gelatin microspheres incorporating bFGF, the number of cells infiltrated into Matrigel increased to a significantly high extent compared with the bFGF co-implantation. Matrigel alone was much less effective in inducing formation of adipose tissue. We conclude that gelatin microspheres incorporating bFGF enable Matrigel to efficiently induce de novo adipogenesis at the implanted site in respect to the formation rate and volume of adipose tissue.