An automated method for control of oxytetracycline (OTC) residues in chicken and bovine muscle, salmon liver, bovine milk and hen egg has been developed. Tissue homogenate, decreamed milk or whole egg solution was dialysed and the dialysate enriched on a small polystyrene column on‐line to HPLC. OTC and the internal standard (tetracycline) were separated on a polystyrene column by ion‐pair chromatography. The column effluent was mixed with sodium hydroxide and irradiated at 366 nm. Monitoring the resulting derivatives with a fluorescence detector (excitation: 358 nm, emission: 460 nm), OTC could be detected at 1 ng/ml in milk, 1 ng/g in egg, 3–4 ng/g in muscle and 8 ng/g in liver. Relative standard deviations at 50 and 200 ng/g (milk: 20 and 100 ng/ml) ranged from 1.6 to 3.1%.