A new method for determining the service life of respirator cartridges has been developed and tested in a laboratory setting. The method involves using small respirator carbon tubes (RCTs) packed with sorbent obtained from a respirator cartridge of interest. The tubes may be taken into an industrial setting and used to evaluate the work environment. A sample tube is placed directly behind the RCT and periodically replaced. This tube acts as a backup section to the RCT. The sample tube can be brought back to a laboratory and analyzed for the contaminant of interest using validated sampling methods specific for the contaminant. Alternatively, a direct-reading instrument can be placed at the exit end of the RCT to obtain "real-time" breakthrough information. The results, when combined with existing sorbent theories, can be used to predict the service life of a respirator cartridge. The advantage of using RCTs is that, unlike respirator cartridges, they can be taken into the field and used with traditional high-flow air sampling pumps. This method is designed to be able to determine the service life of respirator cartridges even when multiple contaminants are present in the workplace. Results of initial laboratory studies, using carbon tetrachloride as a challenge agent, indicated that RCTs were capable of predicting cartridge service life within an accuracy of +/- 15%.