A technique is described for collecting urine from the Dungeness crab, Cancer magister (Dana), a commercially important seafood and an indicator species of aquatic pollution. The technique has been modified from previously published methods to study the role of urinary excretion in the elimination of lipophilic pollutants by the Dungeness crab. The improved urine collection system uses chemically resistant and nonreactive materials that are better suited to pharmacological and toxicological studies than those used in previous methods. The improved method was tested by injecting a vital dye into catheterized Dungeness crabs and by measuring urine flows for 10 days. This technique can be used to determine the urinary excretion of xenobiotics and facilitate the characterization of chemicals and their metabolites accumulated by crabs.