Detection limits are established within a chemical laboratory to designate low-level data that cannot be distinguished from a zero concentration. Higher limits also are used to denote data with low, nonzero concentrations that are too imprecise to report as distinct numbers. Data below both types of limits are reported to the customer as a “nondetect” (<10). Here, the definitions and uses of detection limits are outlined, and methods for using nondetect data in exposure assessments are explained.