A study was made of the effect of parathyroid hormone (PTH) on blood lead (7439921) concentrations in three situations without unusual lead exposures. Serum PTH levels were measured in 50 of 342 bus drivers, 23 with the highest blood lead levels and 24 with the lowest levels. Blood lead levels were measured in eight osteoporotic women before, after 3 weeks and after 1 year of therapy for bone building. Treatment included four 13 week cycles comprising 1 week of therapy with 400 units per day PTH fragment, calcitonin injections for the next 2 weeks and oral calcium supplements for the following 10 weeks. Lead levels were measured in a hyperparathyroid man, 66 years of age, in a 24 hour urine sample and in blood just before and daily for 5 days following chelation (done 2 weeks prior to parathyroidectomy). The same samples were taken 4 months after surgery. Mean blood lead levels in bus drivers were 12.0 and 3.3 micrograms/deciliter (microg/dl) in high and low lead groups, respectively. Mean PTH levels were 34.3 in both groups, and there were no significant differences in mean age, race or blood caffeine levels. Blood lead levels in women prior to bone building therapy ranged from 2.1 to 8.9, mean 6.0microg/dl. There was a mean decrease of 1.7microg/dl after 1 year, which was significantly different from levels before treatment or after 3 weeks. In the hyperparathyroid subject, blood lead was not affected by chelation but was decreased by 50% following parathyroidectomy. The author concludes that normal levels of PTH are unlikely to affect blood lead levels in environmentally exposed adults. Pathologic PTH elevations may increase blood lead by increasing bone activity or gastrointestinal absorption, and bone building therapies may decrease blood lead by decreased absorption or increased movement into bone.