Aerobic mineralization of several different paperboard materials under laboratory-exposure conditions was studied. A novel respirometer was used to titrimetrically determine the kinetics of gas evolution and the rate of biodegradation was quantified by an empirical rate coefficient k. Various bleached paperboard materials studied showed about the same rate (k = 0.14-0.16 days(-1)) and a 50-58 weight percent conversion of substrate carbon into carbon dioxide under the conditions used in the study.