An examination has been made of the blood pressure (BP), saline preference and circulating renin-angiotensin system of spontaneously hypertensive rats (SHR) of the Okamoto strain, normotensive Sprague-Dawley (SD) rats, SHR suckled from immediately after birth on an SD foster mother (SHR-on-SD) and SD cross-suckled on an SHR foster mother (SD-on-SHR). While the BP of SD-on-SHR was not significantly different from that of control SD, SHR-on-SD had significantly lower BP than SHR suckled on their natural mothers. In two-bottle preference tests, neither the saline preference nor total fluid intake of cross-suckled SHR was significantly different from that of SHR controls. While the total fluid intake of SD-on-SHR was not different from that of SD controls, the saline preference of cross-suckled SD was significantly lower than that of control SD. The heart, adrenal and kidney weights of SHR were significantly greater than those of SD, but there were no significant differences between cross-suckled rats and their respective controls. There were no significant differences in plasma renin activity (PRA) or angiotensin converting enzyme (ACE) activity between any groups and these variables did not correlate with each other, with BP or with saline preference. Thus, some factor transferred from the SHR mother postnatally is required for full expression of the elevated BP, but not the exaggerated saline preference of the SHR. Conversely, the saline preference of SD, but not the BP, is altered by cross-suckling.