Oncogene protein detection may be a valuable molecular epidemiological marker of commitment to the carcinogenic pathway in worker populations exposed to carcinogens. This paper reports the use of serum immunoblotting with monoclonal antibodies to oncogene proteins to screen hazardous waste workers with potential carcinogen exposure who employ state-of-the-art work practices and personal protective equipment to minimize real exposures. Two individuals in this cohort were found to be trace positive for the ras oncogene protein in their serum, but this may have been due to their cigarette smoking. These results are contrasted to previous results in hazardous waste workers with real workplace carcinogen exposures.