By means of two biological diffusion methods an oxytetracycline (OTC) content was determined in the tissues of nine calves treated with a single i. m. OTC dose in the quantity of 15 kg-1 body mass. The preparation used for the treatment was Oxymykoin Spofa inj. ad us. vet. For the testing 2 collection strains -- B. cereus var. mycoides (ATCC 11778) and B. subtilis (ATCC 6633) were employed. The method using spore suspensions of the above strains was more sensitive. OTC was quantitatively determined in the samples by reading the standard curves. By evaluation of the two methods the following results were obtained: 5 to 10 days post injection all calves were positive. 15 days after the administration one out of 3 calves was positive. 20 days following the injection both calves were negative. The most frequent residue occurrence was recorded at the injection site, then in the kidney and liver. Spleen lung and bone marrow were completely without any finding. Maximum concentrations were found in the samples from the injection sites and kidney. In the other organs and muscles (noninjection sites) many times lower concentrations were found. Culinary and technological treatment of positive meat and liver samples revealed that already 15 minutes' boiling destroyed the microbiologically active OTC residues; on the contrary, after roasting OTC inactivation in the samples was not that univocal. Freezing and salting are utterly insufficient for OTC inactivation. A preslaughter withdrawal time of 20 days is recommended for the preparation tested.