Although the fluorine in human tissues may exist in both inorganic and organic (covalently bound) forms, the inorganic fraction is clearly the most relevant for assessing human exposure to, and utilization of, environmental fluoride. There is now general agreement that the inorganic fraction of total tissue fluorine can be accurately determined by a variety of analytical techniques. One of the basic questions considered at this workshop is whether the analysis of a specific tissue or body fluid can provide an estimate of how much of the fluoride to which an individual is exposed actually enters and accumulates in the body. The analysis of hair and nails has been used as an indicator of exposure and utilization for several trace elements, including fluoride. Due to methodological uncertainties regarding sampling and pre-analysis treatment, however, it is presently not possible clearly to distinguish fluoride which is incorporated into hair and nails during formation (endogenous) from that which becomes associated with the tissues following exposure to the environment (exogenous). Consequently, although the fluoride content of hair and nails is clearly increased by environmental exposure to fluoride, the conclusion that these tissues are suitable indicators of fluoride utilization and accumulation in the body is premature.