Chlortetracycline was administered to the rabbits per os in a single dose of 150000 Units/kg. After 29-30 days of pregnancy the rabbits were sacrificied 1--3--6--9--12--24-hours and 2--3--4 days after the drug administration. Three-four rabbits were examined in every experiment. The antibiotic levels were determined by the agar-diffusion method. It was found that chlortetracycline was present in bactericidal concentrations in all 60 tissues of the rabbits and fetus examined except the rabbits eye lens. In some tissues of the rabbit and fetus chlortetracycline persisted up to 3 and 2 days respectively. The antibiotic levels in the organs, tissues and fluids of the fetus were many times lower than those in the rabbits. The concentration peak in the fetus was attained somewhat later and the rate of the concentration decrease was lower as compared to the same indices in the rabbit. The highest concentrations of chlortetracycline in the fetus were registered in the amniotic membranes, joints, bones, urine and amniotic fluid.