1 The object of this study was to evaluate hemoperfusion in tricyclic antidepressant (TCA) poisoning. 2 Eight patients with severe TCA-poisoning and one patient with maprotiline poisoning were treated with resin hemoperfusion (HP). All patients were in Grade III or Grade IV coma with a QRS interval of 100 ms or greater. Hemoperfusion was started and continued until a satisfactory clinical response was obtained or for up to a maximum of 4 h. 3 Clearance values and extraction ratios were calculated during HP. The extraction ratio for all drugs was high (0.91-0.98) showing an effective clearance of these drugs from the blood compartment. After termination of HP a rebound effect of blood concentrations was seen in five cases. The total amount of the drug recovered was in no case greater than 3.1% of the estimated amount ingested. 4 It is therefore difficult to ascribe the clinical improvement seen in these patients during HP to the removal of significant amounts of the drug taken.