In this cross-sectional study we examined 200 aluminum potroom workers in Arak, Iran, for their serum calcium, serum parathyroid hormone (PTH), urinary creatinine, and preshift urinary fluoride (F). Individual data were analyzed in relation to age and work duration. The mean serum PTH measured with enzyme linked immuno sorbent assay (ELISA) was 53.84±27.69 pg/mL with 16% of workers having serum PTH assays higher than the upper normal range limit of 76.6 pg/mL. Urinary F measured by the ion selective electrode showed a mean of 2.258±1.426 mg F/g of urinary creatinine, with 46 (23%) of workers having levels more than 3 mg F/g of urinary creatinine. Among the potroom workers, there was a highly significant positive relationship between serum PTH and work duration (p<0.003). These results confirm that excessive chronic F exposure can elevate serum PTH levels.