• We determined minocycline levels in human tears and plasma samples using high-performance liquid chromatography. In the first study, we determined the trough tear and plasma levels of minocycline in patients with active trachoma 24 hours after an oral dose. After a single dose of minocycline, the mean concentration of the drug in tear samples was 189 ± 58 ng/mL and corresponding plasma levels were 578 ± 290 ng/mL. In a second study, we monitored the pharmacokinetics of the drug in tear and plasma samples of healthy nonfasting adults. Tear and plasma samples were collected at 1 through 6, 12, 24, 48, 72, and 96 hours. The pharmacokinetics study revealed that 48 hours following a single 200-mg dose of minocycline, the mean tear level of minocycline was 68 ng/mL, which is above the in vitro minimal inhibitory concentration required for Chlamydia trachomatis and other susceptible organisms.