A new system for the study of angiogenesis in vivo has been devised. It consists of a small disc of polyvinyl alcohol foam, covered on both flat sides by Millipore filters, leaving only the edge as the area for cell penetration into the disc. Angiogenic agonists or antagonists, as well as other substances to be studied, are placed in the center of the disc. The slow release of these substances is maintained by a film of ethylene-vinyl acetate co-polymer, or by the use of agarose. The disc is implanted subcutaneously in the host animal through a distant skin incision. In mice, the optimal times for examination of the discs are 7 to 12 days after implantation for discs containing angiogenic stimulants and 12 to 20 days for those without stimulants. After a period of growth is completed, the disc is removed, fixed, and embedded in paraffin or methacrylate. Medial plane sections, stained by a variety of methods, are used to observe and measure the growth of vessels and stroma into the disc. Whether stimulated or not, this growth is centripetal and can be easily quantitated by simple morphometric technics. This system has already been used in mice, to study the proliferation of vessels and fibroblasts into discs devoid of, or containing angiogenic stimulants (epidermal growth factor, acidic fibroblastic growth factor). We have also utilized the discs to demonstrate the inhibition of vessel growth by hyperthermia. Examples of these applications are presented. The disc angiogenesis system is easy to prepare, inexpensive, and well tolerated, at least by mice. Its simplicity and reproducibility make it suitable for a wide range of applications beyond those described here.