The objective of this study was to investigate the interrelationship between taurine and erythrocyte-membrane NaK ATPase activity. A comparison was conducted to test whether taurine or uric acid (a water-soluble scavenger of free radicals) prevents or recovers the depletion in membrane ouabain sensitive NaK ATPase activity resulting from ozone exposure or cholesterol enrichment of the erythrocyte membrane. A depletion of 44% and 27% in ouabain sensitive NaK ATPase activity was respectively caused by ozone exposure and cholesterol enrichment. Taurine as well as uric acid partially prevented the activity loss from ozone exposure. In addition, taurine at high concentrations (from 1.5 to 4.5 mM) restored the depletion of erythrocyte membrane NaK ATPase activity due to ozone exposure and prevented the depletion of the enzyme activity due to cholesterol enrichment. In contrast, although the same high concentrations were used, uric acid failed to show either of the above effects. These results suggest that taurine acts (1.5-4.5 mM) polyvalently as not only an antioxidizing agent but also as a membrane stabilizer to maintain the functions of membrane Na-K ATPase, a membrane-bound protein.