The tissue distribution of cephalexin, a cephalosporin C derivative, was studied in New Zealand rabbits at 25 days of pregnancy, following oral or i.m. administration. Evidence was obtained that this antibiotic is well absorbed when given orally The placental transfer of cephalexin occurred in both oral and parenteral treatments, however, the drug levels detected in fetal tissues were lower than in the pregnant. Marked differences were observed in the maternal and fetal tissue distribution of the cephalexin between orally- and parenterally-treated rabbits.