The usefulness of measuring fluoride (16984488) in serum and urine as an index of hydrofluoric-acid (144490) (HFA) exposure in workers with chronic renal function failure (CRF) was investigated. The first group consisted of 40 patients with CRF and serum creatinine and blood urea nitrogen values greater than 5 and 50 milligrams per deciliter, respectively. The second group was composed of 120 male workers in the electronics industry who were irregularly exposed to low concentrations of 1 to 3 parts per million HFA. The comparisons consisted of 320 healthy subjects aged 30 to 70 years living in a rural community. For the second part of the study, five patients with CRF were orally given sodium-fluoride (7681494) as 4 milligrams fluoride (16984488) after an overnight fasting. Blood and urine samples were collected before and 0.5 to 96 hours after fluoride administration. Renal clearance of fluoride, the amount of fluoride filtered by the glomeruli per minute, tubular reabsorption of fluoride, and glomerular filtration rate were calculated for patients with CRF. The serum and urinary concentrations of fluoride in patients with CRF and HFA were considerably higher than comparisons. In some patients with CRF, only 6.2 percent of the ingested fluoride was excreted in the urine during a 24 hour period compared to 48.8 percent in the comparisons. Mean serum concentrations of fluoride in CRF and comparisons were similar after 2 hours; urinary concentrations of fluoride, fluoride filtered through the glomeruli per minute, and tubular reabsorption of fluoride in patients were markedly lower than in comparisons. Correlations between clearances of fluoride and creatinine and between renal fluoride and urinary diuresis were good. The authors suggest that engagement in fluoride exposed work and excessive intake of products containing fluoride is contraindicated in workers who have clinical evidence of renal failure if systemic fluoride poisoning is to be prevented.