The antidiuretic effect and pharmacokinetics were investigated in 16 healthy, male overhydrated volunteers after intranasal administration of 20 microg desmopressin. The antidiuretic activity was measured by determination of urine osmolality and diuresis every 15 minutes over a period of 8 hours. Both study preparations were equally effective regarding a rapid onset of activity and a highly reproducible magnitude of effect. Urine osmolalities, analyzed as area under the time curve (AUCosm) and maximum urine osmolalities were similar for both nasal sprays. Urine volume, analyzed as area under the time curve, was raised after treatment with the test preparation. Bioequivalence was assessed for the primary criterion AUCosm by a calculated mean ratio (test/reference) of 102.8% and a 90% confidence interval ranging from 95.4% to 110.8%. Plasma levels of desmopressin, measured by a specific and sensitive radio-immunoassay method, were already detectable 20 minutes after administration. The mean time curves were parallel at different concentration levels. The maximum desmopressin plasma concentrations of both preparations were comparable, showing high interindividual variability. The times of reaching maximum plasma concentrations were similar. Desmopressin bioavailability was increased after treatment with the test preparation (mean ratio of 130.8% and a 90% confidence interval ranging from 109.9% to 155.7%). Both preparations showed a pronounced biological effect with similarly raised urine osmolalities. The detected differences in bioavailability seem to have no direct correlation to the biological response.