The loss of 45 drugs from intravenous solutions during simulated infusions through plastic infusion sets; factors affecting such losses; and ways to minimize these losses are investigated. A total of 43 drugs was studied in 0.9% sodium chloride solution; one drug was in 5% dextrose solution and one in a solvent supplied by the manufacturer. Drug loss was studied in plastic infusion sets, with and without burette chambers, and glass infusion bottles; polyethylene and silastic tubing with glass syringes on an infusion pump; and single-use all-plastic syringes. Variables studied were flow rates, infusion times, drug concentrations, pH, and tubing lengths and radii. Clomethiazole edisylate, chlorpromazine hydrochloride, diazepam, promazine hydrochloride, promethazine hydrochloride, thiopental sodium, thioridazine hydrochloride, and trifluoperazine dihydrochloride were lost from solution during infusions through at least one system. The loss of most drugs during infusion was slow, time-dependent, and concentration-independent, indicating a diffusion-controlled sorption process rather than a binding, adsorptive process. Drug loss was lowest in short lengths small-diameter tubing with low permeability constants. None of the drugs was lost stored in all-plastic single-use syringes. It is concluded that loss of drugs through sorption processes can be minimized by administering infusions through short lengths of small-diameter tubing made of inert plastics.