Clinical and epidemiologic investigations into the etiology of cancer and other chronic diseases are increasingly reliant on laboratory analyses to characterize exposures, susceptibilities, and biological effects in human populations. Obtaining these data for sizeable human populations will require access to large numbers of specimens of human body fluids or tissues. DNA or hemoglobin are commonly needed for the laboratory analyses. For some studies the only available specimens are samples of clotted blood. For example, the Third National Health and Nutrition Examination Survey III (NHANES III) will obtain extensive questionnaire and laboratory data from a stratified multistage probability sample of 15,000 subjects of the U.S. population, including clotted blood from a 70 ml drawn from each adult. This paper presents a method for obtaining DNA and hemoglobin from these whole blood clots. It involves application of widely used methods for red cell lysis, protein digestion, and phenol/water/chloroform DNA extraction. Application of the procedure to specimens currently being collected and discarded by studies such as the NHANES III will provide a unique and cost effective research opportunity to help define the magnitude of human exposure to certain environmental pollutants and investigate susceptibility factors in a large probability sample of U.S. residents, information that could play a critical role in both assessing risk and determining health effects from environmental exposures.