Particulate and bacterial contamination of IV fluids and drugs have been implicated in venous thrombosis, infusion phlebitis, suppurative thrombophlebitis, pyrogenic reactions, and systemic sepsis. In a study of the inflammatory potential of the filterable residue of sodium cephalothin, we have found a tissue-specific reaction with venous endothelium but not with cutaneous or subcutaneous tissues. In a controlled animal model, removal of particulates from an infusion by use of a 0.45 μ in-line membrane filter reduces the incidence and severity of infusion phlebitis.