Organophosphorous (OP) pesticides have been used heavily in the United States and have been detected in dust, handwipes, drinking water, food, and air indicating human exposure pathways. Inside the body, these pesticides are metabolized mostly to one of six alkyl phosphate compounds: dimethylphosphate, dimethylphosphorodithioate, dimethylphosphorothioate, diethylphosphate, diethylphosphorothioate, and diethylphosphorodithioate. These metabolites have been detected in urine and the quantity of these metabolites in urine has been shown to correlate with the pesticide dose that a person has experienced. Therefore, the measurement of these urinary metabolites can be used to evaluate exposure. Unfortunately, this measurement is not straightforward. To characterize the performance of four existing analytical methods used to analyze urine samples for the six urinary alkyl phosphate metabolites of OP pesticides, an interlaboratory comparison study was done.