Male Jcl:SD rats were fed vitamin D2 (ergocalciferol) at levels of 0 (control), 0.39, 0.63 and 1.00% or 0 (control), 0.0195, 0.0315 and 0.050% in the diet for 7 days. All rats of the 0.39-1.00% groups expired on days 2 and 3, while some rats of the 0.0195-0.050% groups died on days 3-6. LD50 (median lethal 7-day cumulative dose calculated from food intake) is 110.5 mg/kg (0.0354% dietarily). In expired and surviving treated rats, several organs (kidney, heart, etc.) were found to be mineralized; there were also renal tubular injuries and pulmonary bleeding. Centrilobular necrosis of liver was detected only in dead rats. Treatment also caused hypercalcemia but did not decrease blood coagulation factors. These results suggest that vitamin D does not have the effect of impeding blood coagulation but that it is extremely toxic, probably due to the hypercalcemia it causes.