In an open, random, cross-over trial, 8 young healthy volunteers were given standard doses of lymecycline and doxycycline for 2 days to achieve steady state. The pharmacokinetics of each tetracycline in serum and dermal, suction blister fluid were determined after oral doses of 300 mg lymecycline or 100 mg doxycycline on the 3rd day. Serum concentrations were higher for lymecycline than for doxycycline, the difference being statistically significant from 3 to 9 h after dosing. Also blister concentrations were higher for lymecycline than for doxycycline, though the difference was not statistically significant. The serum half-life for lymecycline was close to 10 h, for doxycycline 12 h. According to our results, both lymecycline and doxycycline should be regarded as 'intermediate-acting' tetracyclines, and each should consequently be dosed twice daily.