In 20 patients with chronic peripheral vascular disease measurement was made of serum and urine phenol concentrations after lumbar or thoracic sympathetic block with 4-10 ml of seven per cent aqueous phenol. Peak concentration times (tmax), peak concentrations (Cmax), lag times (Tlag), apparent elimination half-lives (t1/2el), and areas under the serum concentration curves (AUC) were determined. The values of tmax, Cmax, Tlag, t1/2el, and AUC were 18.8 +/- 2.5 min, 3.01 +/- 0.28 microgram X ml-1, 5.3 +/- 1.6 min, 30.3 +/- 2.8 min, and 365 +/- 41 micrograms X ml-1 X min-1, respectively, for unconjugated phenol. Values for conjugated phenol were 54.9 +/- 4.5 min, 4.15 +/- 0.25 microgram X ml-1, 9.9 +/- 5.9 min, 64.0 +/- 7.3 min, and 838 +/- 95 micrograms X ml-1 X min-1, respectively. The cumulative urinary excretion in the conjugated form within 8 h ranged from 31 to 63 per cent of the dose administered. The results indicate that phenol has a very short half-life and is excreted quickly into the urine, conjugated with sulfate.