2-Thiobarbituric acid (TBA) was used to measure the degree of beer staling. Optimum conditions were established for the reaction between TBA and stale flavor constituents present in beer, beer extracts, and beer distillates. A correlation existed between the extent of beer staling and TBA values. Results obtained on fresh and stored beers indicated that the TBA test may be used to determine the concentration of TBA reactive compounds present in beer as well as the quantity of TBA reactive compounds that can be produced in a beer upon aging. Several factors influencing the formation of TBA reactive compounds in beer were studied. A number of commercial beers were analyzed by the TBA procedure and were found to possess different levels of TBA reactive compounds. It was also found that TBA test may be used not only to characterize different brands of beer but also to follow product consistency and uniformity.