The distribution of amoxycillin, ticarcillin and clavulanic acid into lymph collected from the right lymphatic duct of rabbits was examined after intravenous administration. The compounds were administered to simulate, in the plasma of rabbits, the concentrations of amoxycillin, ticarcillin and clavulanic acid measured in human serum after the administration of either an iv bolus dose of amoxycillin 1.0 g plus clavulanic acid 200 mg, ticarcillin 3.0 g plus clavulanic acid 200 mg, or an iv infusion of amoxycillin 2.0 g plus clavulanic acid 200 mg or ticarcillin 3.0 g plus clavulanic acid 200 mg given over 30 min. Lymph concentrations of the compounds reached a peak rapidly after the simulation of a bolus dose (0-1 h) and the concentration-versus-time profiles in plasma and lymph were generally similar after 45 min. Following simulation of an iv infusion, peak concentrations of amoxycillin and clavulanic acid in lymph were reached at approximately the same time as for the bolus simulation, but that of ticarcillin occurred slightly later. The elimination half-lives of the compounds were similar in plasma and lymph. The percentage penetration values were high (greater than 80%) irrespective of the concentration-versus-time curve simulated. The penetration of clavulanic acid was compatible with that of the coadministered penicillin agent and was similar when given with either amoxycillin or ticarcillin.