A simple, rapid and precise analytical method for determination of doxycycline in human plasma is described. A high-performance liquid chromatography (HPLC) system based on a mbondapak C18 column (300 mm x 4.6 mm i.d., 10 microns) and a UV detector (lambda = 347 nm) were used. A mixture of actonitrile 0.1 M potassium dihydrogen phosphate buffer (35:65 v/v) adjusted to pH 3 was used as mobile phase. The proteins were precipitated with a 24% perchloric acid aqueous solution. The detection limit for doxycycline in plasma was 3 ng mL-1. The average recovery was about 96%. The method is simple, sensitive and suitable for pharmacokinetic studies of doxycycline. The inter-day and intra-day assay coefficients of variation were found to be less than 8%.