After intravenous administration or nasal feeding of (6, 7-3H)-labelled norethindrone-3-oxime (NETO) or norethindrone (NET) to rhesus monkeys, the serum concentrations were determined by measuring the radioactivity after separation with HPLC. The serum concentrations of total extractable radioactivity were also measured without HPLC separation. In cases of nasal feeding, NETO and NET were quickly absorbed, and almost all of them were eliminated within 24 hours. NETO, when given via both routes, was partly metabolized to NET and partly remained in original form. The blood concentration--time curves for NETO and NET were adequately fitted to two compartment models. No significant difference in pharmacokinetic parameters between the two drugs was observed. The absolute bioavailability for NETO and NET were found to be 64.46 +/- 34.60% and 35.02 +/- 26.49% respectively.