A high-performance liquid chromatographic method for the analysis of doxycycline in turkey plasma samples using demeclocycline hydrochloride as the internal standard was developed, optimized and validated. A one-step extraction procedure and an isocratic HPLC method with UV detection were used. No interferences with endogenous compounds or with the anticoagulant were observed. Linear calibration curves (r2 > 0.99) were obtained in water and plasma between 0 and 600 micrograms ml-1. Good recoveries for doxycycline (> 66%) and demeclocycline (> 72%) were seen both in water and in plasma. The coefficient of variation was < 9.86% for within-day reproducibility and < 7.53% for the between-day reproducibility. The deviation between the mean value found and the true value was < 14.5% (accuracy). The limit of detection was 0.1 microgram ml-1 in plasma samples. A good stability of doxycycline was observed in water and in plasma samples after storage for six months at -20 degrees C (recovery > 91%).