The manual method of Stockhausen, using 6,6'-dithiodinicotinic acid as a specific reagent for SH-groups, has been modified to give an automated kinetic assay. Readings are performed with the LKB Reaction Rate Analyzer 8600 in a volume of 1–2 ml at a rate of 60 samples per hour. For reduced glutathione (as a standard), concentrations between 3 and 60μmole/l can be measured with a mean relative standard deviation of 4.2%; the limit of detection is 1.5μmole/l. Interferences are discussed.