We show that N-acetylcysteine (NAC) has the ability to cause statistically significant diminishment in the in vitro formation of irreversibly sickled cells (ISCs) at concentrations greater than 250 micromol/L. Other antioxidants, approved for human use (cysteamine, succimer, dimercaprol), were not efficacious. NAC had the ability to cause statistically significant conversion of ISCs formed in vivo back to the biconcave shape. NAC was also shown to reduce the formation of dense cells and increase the available thiols in beta-actin. We showed that diminishing reduced glutathione (GSH), by treatment with 1-chloro-2,4-dinitrobenzene, resulted in increased dense cells. We conclude the NAC blocks dense cell formation and ISC formation by targeting channels involved in cellular dehydration and beta-actin, respectively. The efficacy of NAC is probably due to its combined antioxidant activity and ability to increase intracellular GSH.