Synthetic elastomeric polypeptide matrices based on the repeating amino acid sequences of elastin have biophysical and biological properties which are favorable for prosthetic materials. An important requirement envisaged for some applications is the ability to support cell adhesion and growth. The X20–poly– (GVGVP), the γ–irradiation cross-linked elastomeric matrix based on the repeatin poly[n(GVGVP), (GRGDSP)] containing the covalently incorporated cell adhesion sequence Arg–Gly–Asp–Ser (RGDS) were synthesized. These matrices were tested for their ability to support the adhesion and growth of bovine aortic endothelial cells and of bovine ligamentum nuchae fibroblasts. Adhesion experiments carried pentamer Val–Pro–Gly–Val–Gly, and X2 B – out in albumin-containing media showed that matrices containing 60:1, 40:1, and 20:l ratios of (GVGVP):(GRGDSP) supported maximal cell attachment, that matrices containing 100:l exhibited an intermediate level of attachment and that matrices composed of 500:l and (GVGVP) alone were very poor supports for cell attachment. Serum in the media promoted submaximal cell attachment to X20–poly– (GVGVP) but did not permit substantial cell growth. Cell growth was supported by matrices having high ratios of (GRGDSP). Ratios of 60:1, 40:1, and 2O:l supported three population doublings of endothelial cells over 3 days resulting in confluent matrix-adherent monolayers. Ratios of 40:l and 20:l similarly supported the growth of fibroblasts.