The purpose of this work was to identify an accurate, noninvasive biomarker of boron exposure that could be used in worker populations. Occupational exposure to boron is of concern due to high numbers of workers exposed, animal toxicity data suggesting reproductive effects, and lack of human studies. Total daily boron exposure was determined from duplicate samples of 24-hr food and fluid intake, plus workplace personal air monitoring in boron workers and comparison groups in northern China during 2003 and 2004. Boron was also measured in blood, semen, creatinine-corrected postshift urine, and 24-hr urine. Total daily boron exposure (mg/day) averaged 41.2 for men working in the boron industry and 2.3 for the comparison group. Boron concentration in postshift urine was correlated with 24-hr urine boron concentration (Pearson correlation coefficient = 0.85, p < 0.0001). Boron concentration in postshift urine was correlated with total daily boron exposure measured through food, fluid, and personal air monitoring (Pearson correlation coefficient = 0.83, p < 0.0001). Boron concentration in postshift urine was also correlated with internal dose measures of boron in blood and semen (Pearson correlation coefficient = 0.85, 0.80 respectively, p < 0.0001). This work suggests that creatinine-corrected, postshift urine boron concentration can be used as a biomarker of human boron exposure in worker populations.