Twenty-two tolerable upper intake levels (ULs) have been established using data available from research with both humans and animals. No ULs were established for another 10 nutrients for which the existing data were evaluated. Gaps in knowledge on the adverse health effects that may arise as a result of acute, chronic, and lifetime exposures to high levels of many of these nutrients remain. The existence of a UL for a nutrient is not an indication that no gaps in the desired information exist, nor does the absence of a UL suggest that no risk of adverse health effects exists for very high levels of nutrient intake. Finally, it is important to keep in mind the definition of a UL. It is "the highest level of daily nutrient intake that is likely to pose no risk of adverse health effects for almost all individuals in the general population." There are many gaps in knowledge about the levels at which several nutrients cause adverse health effects. As these gaps are filled, the values for ULs will be adjusted as appropriate.