The guidelines (FEDERAL REGISTER 1978) proposed by the Environmental Protection Agency for registration of crop pesticides state that microbial function studies must include data on the effects of a pesticide on nitrogen fixation, nitrification, and degradation of cellulose, starch and protein. These function tests must be sensitive, rapid, easily executed, versatile and capable of monitoring metabolism of microorganisms in a soil sample. Because a suitable method was not currently available for monitoring cellulose and starch degradation, we have developed a function test based on radiorespirometry, a methodology used extensively in our laboratory for extraterrestrial life detection (LEVIN 1962, LEVIN and STRAAT 1976a, LEVIN and STRAAT 1976b), clinical identification of microorganisms (SCHROT et al., manuscript in preparation) and rapid detection of bacteria in water (LEVIN et al. 1956) and in blood (SCHROT et al. 1973). This rapid and sensitive technique is readily applicable to monitoring starch and cellulose metabolism in soils. The method described herein quantatively measures microbial cellulose degradation by ~nitoring metabolically evolved - C02 following addition of C-labeled cellulose or starch to the soil sample.