Activated protein C (APC) is a highly specific serine proteinase which functions as an important naturally occurring antithrombotic enzyme. APC also has antiinflammatory properties. We have developed a large-scale process for the production of APC for therapeutic use starting with cryoprecipitate-poor human plasma. This report describes the process, its performance at the pilot plant scale, and the characteristics of immunoaffmity-purified human APC concentrate referred to as APC (human). The process consists of three chromatographic steps, an enzymatic conversion step, and incorporates a solvent/detergent treatment step for the inactivation of lipid-enveloped viruses. Solvent/detergent was shown to rapidly inactivate spiked HIV-1, as well as three marker viruses to nondetectable levels under process conditions. The immunoaffmity-purified protein C (PC) intermediate was enriched 13,600-fold over plasma and had a specific activity of 231 U/mg. The overall yield of the process following enzymatic conversion of the PC intermediate to APC and its processing by anion exchange chromatography was 36%. APC (human) was shown to be highly purified, functional and stable.