A commercial formulation of chloramphenicol and oxytetracycline was administered to dairy cows and bullocks by the intramuscular route. Concentrations of drugs were determined in milk and edible tissues by high‐performance liquid chromatographic and microbiological methods. The data allowed the calculation of withdrawal times for milk (4 and 17 milkings for chloramphenicol and oxytetracycline, respectively) and for tissues (35 days for chloramphenicol, more than 35 days for oxytetracycline, depending on the levels at the injection sites). Hence oxytetracycline residues were the most persistent in these types of foods, according to our dosage scheme.