The sorption of clonazepam to polyvinyl chloride tubing, polyethylene-coated tubing and to a polyethylene syringe was determined. Pumping of clonazepam (5 mg/48 ml) through the polyvinyl chloride tubing with flow rates of 2 ml/h and 4 ml/h resulted in a reduction of the clonazepam concentration to about 40% and 55% of the original strength after 0.6 h, respectively. This value was 55% at a flow rate of 2 ml/h and a clonazepam concentration of 10 mg/48 ml. The effluent clonazepam concentration increased gradually after an infusion period of 1 h. Sorption of clonazepam to the polyethylene syringe and to the tubing coated on the inside with polyethylene does not occur. The use of polyethylene-coated administration sets is recommended for intravenous administration of clonazepam.