Treatment of Ehrlich ascites cells in vitro with increasing concentrations of cysteamine, AET or glutathione (GSH) resulted in a proportional increase of the intracellular level of non-protein-bound sulphydryl (NPSH). At equimolar concentrations, the increase in NPSH was greatest after AET-treatment, less after cysteamine and least after GSH. A considerable part of the increase in NPSH after AET- and cysteamine-treatment was due to an increase in content of cellular GSH. The increase in intracellular NPSH after GSH treatment was, in part, due to some compound(s) other than GSH.

After interruption of AET or cysteamine treatment, the total NPSH content of the cells decreased immediately, but the GSH level continued to increase for some time before it also started to fall.

The results were interpreted as indicating that intracellular release of GSH may be a major mechanism for the radioprotection afforded by the substances used in the investigation.