The efficacy of intermittent charcoal haemoperfusion in combination with forced diuresis and Prussian blue therapy was evaluated in three cases of thallium poisoning. At a blood flow of 300 ml/min the average blood clearance values obtained with haemoperfusion were 72 +/- 11 ml/min (mean +/- SD) at a starting blood concentration above 2 mg/l and 120 +/- 23 ml/min (mean +/- SD) below this blood level. As a result of the combined intensive treatment, the thallium half-lives in blood observed during the period monitored were only 25-41 h. Removal of thallium by haemoperfusion is faster per unit of time than simultaneous excretion by forced diuresis. When forced diuresis was combined with intermittent (4-20 h intervals) haemoperfusion therapy, the total elimination by each technique was about equivalent over the period of combined treatment. Saturation of the Adsorba 300 C columns occurred during treatment. As a result, the clearance obtained did decrease to half the initial value in 2-3 h. As this decrease in efficacy is related to the blood concentration, haemoperfusion is more efficient at lower blood concentrations. This is in contradistinction to forced diuresis, of which the excretion is proportional to the blood concentration.