Glutathione (GSH) and glutathione disulfide (GSSG) are biologically important intracellular thiols; alterations in the GSH/GSSG ratio are often used to assess exposure of cells to oxidative stress. Although several methods are available for measuring GSH and GSSG, all have some disadvantages including the need to generate derivatives, the inability to conveniently measure both GSH and GSSG, and a lack of sufficient sensitivity to allow detection in very small samples/cells of extrahepatic tissue. These studies present a rapid, validated HPLC-electro-chemical method for determining GSH and GSSG in small samples such as those from microdissected airways of the mouse containing 50-200 micrograms protein which is suitable for routine use. GSH and GSSG can be measured at levels of 1 and 2 pmol on column, respectively, with acceptable accuracy and precision and without the need to generate derivatives. In microdissected airways from the mouse, the intraday assay coefficient of variation for GSH varied from 4.7 to 5.9% and for GSSG was 4.4 to 5.7%. The interday assay coefficient of variation ranged from 6.0 to 7.6% for GSH and 5.5 to 23% for GSSG. The effects of repeated freezing and thawing on the concentrations of GSH and GSSG indicate that multiple cycles do not significantly alter the GSH or GSSG concentration as the number of cycles increases. Addition of GSH or GSSG to samples increased the peak areas appropriately, without altering the peak shape, retention time, or peak area of the corresponding reduced (oxidized) thiol. The ratio of GSH/GSSG in freeze-clamped liver ranged from 46 to 248, while liver tissue which was homogenized fresh had GSH/GSSG ratios of 62-150. The technique appears to be capable of reproducibly measuring GSH and GSSG in small quantities of nonhepatic tissue.