The effects of atrial natriuretic peptide (ANP) on urinary protein excretion were examined in patients with renal parenchymal diseases (RPD, n = 18) and those with diabetes mellitus (DM, n = 12). Before and 30 min after intravenous injection of ANP (50 micrograms), urine samples were collected. ANP injection increased urinary volume and urinary sodium excretion in both groups. In RPD, urinary protein excretion (UprV) increased by 87% (1.5 +/- 0.7 [SEM] to 2.8 +/- 1.1 mg/min, p less than 0.05). ANP also increased UprV in patients with diabetic nephropathy [N(+); 1.7 +/- 0.8 to 5.0 +/- 2.5 mg/min, p less than 0.05] and those without nephropathy [N(-); 0.10 +/- 0.02 to 0.22 +/- 0.07 mg/min, p less than 0.05]. Since ANP increased creatinin clearance in both groups (+9.4 +/- 2.5 ml/min in RPD and +24.1 +/- 3.5 ml/min in DM, p less than 0.01 for both), urinary protein to creatinine excretion ratios (UprV/UcrV) were determined, which should be a parameter of glomerular protein permeability. The UprV/UcrV ratio increased by 48% (p less than 0.01) and 24% (p less than 0.05) in RPD and in DM, respectively. ANP did not change urinary composition of albumin and globulin. In RPD, increases in UprV by ANP were positively related to the basal serum creatinin levels (r = 0.57, p less than 0.01). In DM group, ANP-induced increases in the UprV/UcrV ratio were higher in the N(+) subgroup than in the N(-) subgroup (+0.8 +/- 0.4 vs +0.09 +/- 0.04, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)