44 patients receiving regular hemodialysis therapy were investigated using M-mode echocardiography and systolic time intervals to examine the effects of parathyroid hormone (PTH) and vitamin D on left ventricular function. 12 patients were treated with 1 µg daily of 1α-hydroxycholecalciferol for 6 weeks, which produced a decrease in plasma PTH concentration from 1,883 ± 226 to 1,123 ± 289 ng/l. Fractional fibre shortening (FS) increased from 34.6 to 37.6% (p < 0.025) and mean velocity of fibre shortening (Vcf) increased from 1.21 to 1.32 circ/s (p < 0.01). A second group of 20 patients was studied before and after the plasma magnesium concentration was increased from 1.25 to 1.70 mmol/l, resulting in a fall in plasma PTH concentration from 546 to 418 ng/l (p < 0.001). This was associated with an increase in both FS from 32.4 to 34.3%, and Vcf from 1.19 to 1.21 circ/s. A third group of 6 patients with severe hyperparathyroidism underwent total parathyroidectomy, FS increased from 34.9 to 36.3% and Vcf increased from 1.22 to 1.38 circ/s. In conclusion, our results indicate that vitamin D and PTH do influence left ventricular function in uremic patients on chronic hemodialysis, and that a reduction in plasma PTH levels is beneficial to the uremic he