Distribution regularities of cephalexin and cephradine, 2 semisynthetic cephalospor in antibiotics for oral use were studied on rats. It was found that the cephalosporins had a capacity for satisfactory penetration through the histochematological barriers. The drugs were rather rapidly absorbed from the gastrointestinal tract of the rats into the blood. Their maximum blood levels were determined 1 hour after the administration. The highest cephalosporin concentrations were detected in the kidneys and liver. Still, the level of cephradine in the kidneys was lower and that in the liver was higher than the levels of cephalexin. The lowest concentrations were found in the skeletal muscles. The character of cephradine distribution in the lungs, heart and spleen differed from that of cephalexin; the maximum concentrations of cephradine in these organs were achieved 1 hour after its administration, while those of cephalexin were achieved in 30 minutes. The antibiotics were not detected in the brain tissue. No increase in the concentration gradient with time was observed.