Two distinct quantitative indirect ELISAs were developed to determine the concentration of recombinant cellulase enzymes in culture filtrates. A monoclonal antibody (E1P7) was used as the primary antibody in developing an ELISA specific for Acidothermus cellulolyticus E1 endoglucanase. Likewise, a polyclonal rabbit serum (Ab684) was used to develop an ELISA specific for Thermomonospora fusca E(3) exoglucanase. Dose-response curves indicated a dynamic range for both assays between 0.01 and 0.08 mu g/mL (1-8 ng/assay) when purified enzymes were used as standards. These assays have been used to estimate concentrations of secreted recombinant E1 and/or E(3) in culture supernatants of Streptomyces lividans strain TK24 in which the corresponding genes have been cloned and expressed.