An intravenous dose of 3.0 g ticarcillin and 0.2 g clavulanic acid was given to 11 healthy human volunteers in whom peripheral lymph, serum and urine were monitored for 8 h. The concentrations were assayed microbiologically. The mean levels in lymph collected during the period 0-1 h was 39.3 mg/l of ticarcillin and 2.93 mg/l of clavulanic acid. The mean peak concentration in lymph (appearing between 1.25 and 2.25 h) was 66.3 mg/l for ticarcillin and 4.1 mg/l for clavulanic acid. Elimination was slightly slower from lymph than from serum, the half-life being only 1.04 times longer from lymph than from serum for ticarcillin, but 1.22 times longer for clavulanic acid. The total areas under the concentration curves in lymph was 58% of the serum value of ticarcillin and 81.0% of clavulanic acid. This reflects the ability of the substances to penetrate to lymph. The mean 8-h urinary recovery was 63.7% of the dose of ticarcillin and 43.8% of clavulanic acid. The total body clearances were 14.61/h for ticarcillin and 7.91/h for clavulanic acid and the corresponding d beta distribution volumes 12.21 and 19.11. The ratio of the concentrations of ticarcillin to clavulanic acid in all body fluids increased with time. Pharmacokinetically, clavulanic acid is well suited to be given together with ticarcillin.