A method for the determination of o-toluidine (95534) and aniline (62533) in the urine of workers occupationally exposed to amines was described. Urine samples were hydrolyzed by sodium-hydroxide, extracted with butyl-chloride and hydrochloric-acid, and the concentrations of the two amines in the aqueous phases were determined by high performance liquid chromatography and colorimetric electrochemical detection. The average recoveries of o- toluidine and aniline from field samples were 91% and 100%, the precision was 13% and 16% relative standard deviation, and the limits of detection were 0.6 and 1.4 micrograms/liter, respectively. Method performance was assessed by analyzing 171 specimens acquired during the field investigation. Analysis of urine specimens from chemical factory workers by this method demonstrated median preshift values for o-toluidine for exposed workers of 11 micrograms/liter and for nonexposed workers of 0.7 micrograms/liters. The median postshift value for exposed workers was 65 micrograms/liter, while that for nonexposed workers was 2.6 micrograms/liters. The median values seen for aniline were 11 micrograms/liter for preshift exposed, 2.0 micrograms/liter for preshift nonexposed, 23 micrograms/liter for postshift exposed, and 3.2 micrograms/liter for postshift nonexposed. The ruggedness of the method was tested by variations of eight procedural steps. The authors conclude that a significant uptake and accumulation of these amines occurred during and across workshifts based on the results obtained from the method.