Microsurgical models of vein-to-artery graft surgery have been developed in rats as a means of assessing vein graft adaptation and neo-intimal hyperplasia. Neo-intimal hyperplasia in these grafts is often attributed, at least in part, to an adaptive response by venous smooth muscle cells to the increased intraluminal pressure of the arterial pressure. However, considerable evidence suggests complete or near-complete cellular replacement in these grafts. A series of experiments were undertaken in which male vein or artery grafts were placed into either allogeneic female nude rat hosts or into syngeneic WKy female hosts as a means of determining donor cell survival. Grafts were removed at postsurgery week 2 or week 6 and the fate of the donor male cells assessed by PCR amplification of the testis-determining gene Sry. The SU gene was undetectable in 2-week male to female vein grafts. When left for 6 weeks, donor cells were detectable in vein grafts only after multiple 50-cycle PCR analyses. Minimal donor cell survival was not due to an allograft response, as donor male cells were readily detectable in WKy male to female nude rat artery-to-artery grafts. These data were not nude rat specific, as poor donor cell survival was also evidenced in syngeneic male to female vein-to-artery grafts. In conclusion, we demonstrate only marginal survival of donor cells in rat vein-to-artery grafts. Neointimal hyperplasia in these grafts was not a consequence of donor venous smooth muscle cell proliferation.