BACKGROUND Since 1947, the National Labour Inspection Service in Denmark has relied upon urinary measurements of trichloroacetic acid (TCA) in surveys of the occupational exposure to trichloroethylene (TCE). METHODS We examined the paper files relating to 2397 TCA measurements to extract information about the year, the company, the work process and the worker. We used multiple regression models to analyze the effects of various factors on the urinary concentration of TCA. RESULTS The regression analyses showed that (1) a four-fold decrease in TCA concentrations occurred from 1947 to 1985; (2) the highest concentrations were observed in the iron and metal, chemical, and dry cleaning industries; (3) TCA levels were two times higher among men compared with women in the iron and metal and dry cleaning industries; (4) TCA concentrations were higher among younger compared with older workers; and (5) persons working in an area in which TCE was used, but not working with TCE themselves, also showed urinary TCA levels indicative of exposure. CONCLUSIONS Calendar year, type of industry, degree of contact with TCE, sex and age were predictors of TCA concentration in the urine of Danish workers.