In recent years, studies have shown that non-HLA antigens can be involved in renal graft rejection. The so called minor antigens have been found to be expressed on a variety of cells, including endothelial cells. With the aim of understanding better the role of minor antigens in graft rejection, we undertook a Western blot screening of sera from patients waiting for or having received grafts from living-related or cadaveric donors. In this study we described the reactivity of these sera against a 17 kD antigen with expression in many different cell types.