The distribution of cephalexin in bile and in the gall bladder was investigated in humans after administering pivalexin--a new cephalexin derivative--that exhibits favourable pharmacokinetic characteristics versus cephalexin itself. Two groups of subjects were given either pivalexin or cephalexin in the form of capsules in a single oral dose. Pivalexin in view of its greater excretion of cephalexin in bile and its satisfactory fixation of cephalexin in the gallbladder, as compared with cephalexin itself, may reasonably be regarded as a recommendable antibiotic in the treatment of biliary-duct infections.