Two commercially available long-acting oxytetracycline hydrochloride formulations (Primamycin LA (Pfizer) and Terrallent 20% LA (I.E. Ulagay)) were administered by the intramuscular route to 20 clinically healthy sheep at a dose of 20 mg/kg. The study was performed in a two-period crossover design. Plasma samples were analysed by high-pressure liquid chromatography. The mean maximum concentrations (C-max) was 8.00 +/- 2.05 mu g/ml and 8.61 +/- 1.42 mu g/ml, respectively. The mean area under the concentration time curve (AUC) values were 154.95 +/- 50.37 (mu g h)/ml and 161.70 +/- 47.02 (mu g h)/ml, respectively. The 90% confidence intervals for the ratio of C-max and AUC values for the test and reference product are within the interval 70-143% for C-max and interval 80-125% for AUC proposed by EMEA. It was concluded that Primamycin LA and Terralent 20% LA formulations are bioequivalent in their rate and extent of drug absorbtion.