The exposure of pharmaceutical plant workers, involved in drug compounding and drug production, to 5-fluorouracil (5FU) was studied. 5FU was found by the analysis of air and wipe samples. During weighing, 5FU was detected in the air (75 μg/m3). 5FU was also present on the filter of the mask of the weigher (120 ng). Before drug compounding 5FU was found on the floor (range, <1 to 8 ng/cm2; median, 2 ng/cm2). After routine cleaning significant higher amounts of 5FU were measured (range, 70 to 630 ng/cm2; median, 150 μg/cm2; P = .02). The amounts of 5FU present on several objects were lower when compared to the amounts on the floor. The gloves used were always contaminated (range, 22 to 720 μg/pair of gloves; median, 141 μg/pair of gloves). The uptake of 5FU was established by the determination of α-fluoro-β-alanine, the main metabolite of 5FU, in the urine of the workers. Fifty micrograms of α-fluoro-β-alanine were found in urine of the weigher.