For biomonitoring DNA damage, an optimal method should be capable of detecting many classes of DNA damage in a variety of cell types, provide data at the level of the individual cell, and be sensitive, rapid, and cost effective. An alkaline microgel electrophoresis assay has been developed that may fulfill these criteria. The single cell gel (SCG) assay detects, in individual cells, the presence of single strand breaks and alkali-labile sites. Advantages of this technique include: 1) data are collected at the level of the individual cell; 2) small numbers of cells are required; and 3) the assay is relatively sensitive, simple, and cost effective. The proposed research will continue to characterize the applicability of this technique as a biomarker for DNA damage in humans who potentially have been exposed to biohazards by conducting in vitro studies to assess sensitivity and specificity, and in vivo studies to assess the applicability of the assay to occupationally exposed workers. When fully characterized, this technique will allow for the monitoring of human populations based on microsampling (i.e., fingerprick blood samples). This capability could result in the widespread application of this technique in clinical, environmental, and occupational situations.