Three dosages of calcitriol (10, 30 and 60 IU/day) were given to rabbits by subcutaneously implanted osmotic pumps. The purpose was to compare the dosages with regard to their putative effect in elevating serum aluminum levels by mechanisms such as enhancing intestinal absorption, diminishing renal excretion, or others. To establish uniform levels of endogenous calcitriol and its precursors, all rabbits had been depleted of vitamin D. The depletion was demonstrated by their serum calcidiol and calcitriol levels declining to unmeasurable levels, following the regimen of a vitamin D-free diet. The 8 rabbits were then placed on an aluminum-supplemented (aluminum lactate) ration. The amount of feed (and aluminum) consumed was determined at daily intervals. Serum aluminum levels were determined at intervals during the 7 days on this regimen. In a second test, the same 8 rabbits received the same regimen but in addition were infused with 10, 30 or 60 IU calcitriol per day. It was found that the aluminum-fed rabbits receiving 60 IU/day and 30 IU/day calcitriol infusions showed statistically significantly elevated serum aluminum levels as compared to their levels without calcitriol (p = 0.0208 and p = 0.434, respectively). Rabbits receiving pumps delivering 10 IU/day while receiving the aluminum-supplemented ration showed no rise in serum aluminum with time or treatment during the 7 day study. Likewise rabbits receiving aluminum-supplemented rations without calcitriol showed only an early minimal rise in mean serum aluminum which returned to the pre-test level by the end of a week in spite of continued consumption of aluminum-supplemented rations.