Active infection with one of the herpes viruses, Cytomegalovirus, clearly worsens renal allograft survival. In the present study serologic evidence of infection with another herpes virus, Herpes simplex, was compared with graft survival in 89 cadaveric renal graft recipients transplanted during a two-year period at the Aarhus Center. With respect to Herpes simplex complement-fixing serum antibody status post-transplant, three groups could be identified: 1) No change in antibody titer (25 patients); 2) Significant (4-fold) or more antibody rises (41 patients); 3) No demonstrable antibody (23 patients). Actuarial graft survival was not significantly different in the three groups and thus Herpes simplex infection, in contrast to Cytomegalovirus, does not appear to influence the outcome of renal allograft transplantation.