The compounds 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methoxy-3,6-dichlorobenzoic acid (dicamba) are herbicides commonly used to control a variety of broadleaf plants. An acute poisoning case was recently investigated by the Hawaii Community Study on Pesticides in which the victim intentionally ingested a formulation containing 2,4-D and dicamba. The occurrence of this attempted suicide created a need for a rapid and sensitive method for detecting these compounds in small amounts of human blood and urine. The Hawaii Community Study on Pesticides uses the method of Bevenue et al. to determine pentachlorophenol (PCP) residues in human blood. In an evaluation done by this laboratory, the procedure was shown to be rapid, accurate, sensitive and reproducible. Because 2,4-D and dicamba display chemical characteristics similar to those of PCP, these compounds are also detected by the procedure.