A simulated aerospace study was conducted to assess the biochemical effects of space flight by determining the volume of urine output of each crewman. The Apollo urine transport system (UTS), using a radioisotope, tritium, dilution technique, was tested by four human male subjects. The Apollo UTS met minimum requirements for 14 days even when a single unit was used by four individuals. The best individual performance by a subject gave a ratio of 101.4 plus or minus 4.6%. The overall value for volume measurement from the four subjects was 100.6 plus or minus 4.6%. Any void volume may be calculated by this radioisotope method with the UTS system plus or minus 10% of its volume at the 95% confidence level. One experimental error was the incomplete mixing of the radiosotope. The practicability of this procedure in actual space missions still has to be determined. (Author).