Renal water and electrolyte handling and related plasma hormone levels were measured in male and female New Zealand genetically hypertensive and normotensive rats, in an attempt to establish any potentially important sex-related differences in these parameters. Male hypertensive rats had higher blood pressure than female hypertensive rats, but normotensive rats showed no such sex difference. Both groups of males had higher fluid turnover rates than respective females, and this was associated with raised plasma vasopressin in hypertensive males. Female hypertensive rats excreted more sodium, potassium and chloride in association with lower plasma aldosterone and higher corticosterone levels compared with the other groups. Plasma electrolytes did not differ between the four groups, but plasma osmolality was higher in hypertensive than normotensive rats of both sexes. A higher rate of electrolyte loss and lower fluid turnover in association with reduced plasma vasopressin may contribute to the lower blood pressure of female compared with male hypertensive rats.