The pattern of circulating calcitonin (CT) has been studied in relation to other humoral factors (PTH, calcium, phosphate and magnesium) in patients with chronic renal failure on either conservative or dialysis treatment. The latter group was studied before and after dialysis. In both groups, in basal conditions there was a significant increase in the circulating levels of CT, PTH, phosphate and magnesium and a significant decrease in calcemia compared to control group values. Positive correlations were found between increased CT and PTH and between CT and phosphate in uremic patients on conservative medical treatment, but not in those on hemodialysis. In the hemodialyzed group, the postdialysis increase in calcemia was significantly correlated to an increase in calcitoninemia. These data would indicate that even in severe uremia parafollicular cells are still able to increase CT secretion in response to physiological stimuli.