Injection of atrial natriuretic peptide (ANP) induces marked diuresis, natriuresis and less marked blood pressure reduction. These effects are similar to those of renal kallikrein-kinin system (rKKS). In this study we investigated the influence of ANP on rKKS of rats. ANP was injected intravenously in male normotensive (WKy) and spontaneously hypertensive rats (SHRsp) as a bolus of 3.5 micrograms atriopeptin III. ANP induced, in both groups of rats, a marked increase in diuresis and natriuresis, while blood pressure decreased significantly. Renal plasma flow and urinary excretion of potassium increased only a little. The observed changes were similar in both strains of rats and there was no statistically significant difference except the lower potassium stimulation in the SHRsp than in the WKy (p less than 0.05). In regard to the basal activity of the rKKS there was a significant difference between the two strains of rats. The activity of renal kallikrein in urine and of kininase II in plasma was reduced in the SHRsp about 50%, while renal kinin excretion in urine was markedly enhanced in these rats, if compared to the WKy controls. In both groups of rats renal kallikrein and kinin excretion was stimulated by ANP for a short time and, simultaneously, total kininogen in plasma decreased after the injection of ANP. The increment of renal kallikrein excretion in urine was much less marked in the SHRsp than in the WKy rats. The reduced kallikrein stimulation was compensated by the reduced kinin degradation by kininase II in these rats.(ABSTRACT TRUNCATED AT 250 WORDS)