Male Sprague-Dawley rats were uninephrectomized and given either deoxycorticosterone (DOC) pivalate (12.5 mg three times weekly) and 1% NaCl/0.2% KCl to drink for 4 weeks (DOC-treated), after which DOC was stopped and tap water substituted (post-DOC), or tap water to drink throughout (controls), DOC treatment increased blood pressure, serum sodium, plasma atrial natriuretic peptide (P-ANP) and plasma deoxycorticosterone (P-DOC) (P less than 0.05), while serum potassium, plasma renin and plasma angiotensin II were lower (P less than 0.05) than in control animals. Plasma vasopressin (P-AVP) was also raised but not significantly. These changes persisted for up to 4 weeks post-DOC and, in the case of plasma renin, plasma angiotensin II, P-AVP and P-ANP, for up to 12 weeks. Total body sodium was also increased at 2 weeks post-DOC (P less than 0.05). Rats which were adrenalectomized after 4 weeks of DOC treatment in which DOC injections were stopped, then drank either NaCl/KCl or tap water; blood pressure and P-DOC remained elevated while plasma renin remained suppressed. There were more deaths in rats given NaCl/KCl (five of six) than in the group given water (one of six). Rats treated with a subcutaneous DOC silastic implant had a comparable rise in blood pressure to rats given DOC injections. However, after removal of the implant, while blood pressure remained elevated, P-DOC levels were not raised and plasma renin rose to control levels after 4 weeks. These findings indicate that, in rats given DOC injections, post-DOC hypertension results from sodium and fluid retention as a consequence of chronic hangover of exogenously administered DOC.