A Total Organic Carbon (TOC) Analyzer has been developed for a Life Sciences Risk Mitigation Flight Experiment to be conducted on Spacehab and the Russian space station, Mir. Initial launch is scheduled for December 1996 (flight STS-81). The analyzer will be tested on the Orbiter in the Spacehab module, including when the Orbiter is docked at the Mir space station. The analyzer is scheduled to be launched again in May 1997 (STS-84) when it will be transferred to Mir. During both flights the analyzer will measure the quality of recycled and ground-supplied potable water on the space station. Samples will be archived for later return to the ground, where they will be analyzed for comparison to in-flight results. Water test samples of known composition, brought up with the analyzer, also will be used to test its performance in microgravity. Ground-based analyses of duplicates of those test samples will be conducted concurrently with the in-flight analyses.The analyzer is adapted from commercially successful technology, originally developed in 1991 for a TOC analyzer for Space Station Freedom's Crew Health Care System (CHeCS). The analyzer measures TOC, Total Inorganic Carbon (TIC) and Total Carbon (TC). The analytical range for each of these parameters is from 1 to 50,000 μg/L. The analyzer's capabilities have been augmented to include measurement of pH (from 0 to 14 pH units) and conductivity (from 1 to 200 μmho/cm). Fluid handling and gas/liquid separation features required for enhanced reliability in microgravity have been incorporated into the design, along with features needed to satisfy the safety requirements of the joint U.S./Russian space program.This paper reviews the design, operation and performance of the prototype analyzer. The flight unit is projected to weigh 49 lb, occupy 1.6 ft3, and consume only 41 W of power.