The assessment and cleanup of hazardous waste sites has become a growth industry. Unlike traditional factory employment, chemical exposures on wastes sites are likely to involve uncharacterized mixtures. Medical surveillance of hazardous waste workers has become a major preventive strategy. To evaluate the effectiveness of the traditional laboratory tests employed in most surveillance programs, we compared test results in two groups of hazardous waste workers (409 males, 68 females) with responsibilities for the assessment and management of waste sites. We stratified employees into a group with a high potential for exposure ("exposed") and a group with a low potential for exposure ("unexposed"). Fifty-five clinical chemistry, hematologic, and urinalysis variables were contrasted using an analysis of variance. The only consistently significant difference was a low mean corpuscular volume in the "exposed" group. The lack of other significant findings suggests that either the true exposure status of individuals was not reflected in our classification or that the traditional tests were inappropriate or insensitive. We conclude that it is essential to evaluate surveillance results carefully and to develop protocols that are appropriate to the actual exposures encountered in hazardous waste work.