This study examined plasma levonorgestrel (LNG) concentrations and pharmacokinetics following oral administration of a single LNG 0.75 mg tablet. Sixteen healthy female volunteers 19-44 years old enrolled in the study. Serial blood samples were drawn over 72 h after dosing in a fasting state. A gas chromatographic, negative ionization mass spectrometric detection analytical method was used to determine plasma LNG concentrations. The observed mean peak plasma LNG concentration was 14.1 +/- 7.9 ng/mL (range 6.7-39.0 ng/mL). The mean time of peak concentration was 1.63 +/- 0.74 h (range 1-4 h). The plasma LNG concentration versus time profiles were subjected to noncompartmental pharmacokinetic analysis for the purposes of determining half-lives, apparent oral clearances (Cl/F), apparent volumes of distribution after oral administration (V/F), and mean residence time (MRT). Half-lives calculated from the terminal decline in plasma LNG concentrations ranged from 16.2 h to 32.3 h (mean = 24.4 +/- 5.3 h). The Cl/F was 7.06 +/- 2.69 L/h, V/F was 260 +/- 129 L, and MRT was 27.8 +/- 5.2 h. LNG was well tolerated; there were no serious adverse events during the study.