Single transplanted kidneys from spontaneously hypertensive rats (SHR) have been shown to elicit hypertension in genetically normotensive recipients. This study was designed to investigate the effects of single transplanted kidneys from genetically normotensive donors [Biobreeding (BB)/Ottawa Karlsburg (OK) rats] on blood pressure in SHR recipients. The following groups were formed: group 1 (n = 11), SHR donors and SHR recipients; group 2 (n = 15), BB/OK donors and SHR recipients; and group 3 (n = 8), BB/OK donors and BB/OK recipients. Recipients received antihypertensive treatment (hydralazine) from weaning until renal transplantation at the age of 9 wk and immunosuppressive treatment (anti-CD4 antibody and cyclosporine A) for 3 wk starting on the day of transplantation. Six weeks after transplantation, intra-arterially measured blood pressure and heart weight-to-body weight ratio were highest in group 1, intermediate in group 2, and lowest in group 3. There were no significant differences with respect to plasma urea and creatinine concentrations among the three groups. These results support the hypothesis that hypertension in renal-transplanted SHR depends in part on the genetic background of the transplanted kidney.