Whether the postobstructive diuresis can in part be related to an altered regulation of Dendroaspis natriuretic peptide (DNP) was investigated. Male Sprague-Dawley rats were bilaterally obstructed of their ureters. Control group was with sham ureteral obstruction. Forty-eight h later, tissue levels of DNP immunoreactivity were determined in the plasma, heart, and kidneys. Urine samples were collected in some rats under anesthesia. The plasma DNP immunoreactivity was significantly increased by 45% in the experimental group. The tissue levels of DNP immunoreactivity in the atrium, ventricle, or kidneys did not significantly differ between the experimental and control groups. The urinary flow and sodium excretion rate were 3- to 4-fold increased in the experimental group. The urinary DNP excretion was also increased in the experimental group, which was positively correlated with the urinary volume and sodium excretion. The urinary excretion of cGMP was 2- to 3-fold increased in the experimental group. These results indicate that an enhanced DNP activity may in part be causally related to the postobstructive diuresis.