A randomized prospective study of the effect of medium-chain triglycerides (MCT) upon the absorption and retention of major minerals and nutrients, as well as upon 25-hydroxy vitamin D levels, was performed in low-birth-weight infants. Ten infants received a highcalcium and vitamin D-containing formula, which contained 50% of its fat as MCT, while ten other infants received a similar formula in which all the fat was in long-chain triglycerides. There was a five-day delay in reaching full oral feeding volumes, and therefore there was a delay in the onset of the balance study in the MCT group, primarily due to gastrointestinal symptoms. There was a significant improvement in the percent of fat absorption (P < .05) with MCT, but no difference in the percent of absorption or retention of calcium, phosphorus, sodium, or nitrogen. 25-Hydroxy vitamin D levels decreased in both groups after full oral feeding volumes had been established, but all values were within normal ranges. At the high intake levels of calcium and vitamin D given to the infants, MCT did not increase major mineral or nutrient absorption.