The nickel concentration in fingernails from 2 groups of people occupationally exposed to nickel was determined. In one group, comprising 83 persons moderately exposed to nickel, the mean +/- standard deviation (SD) was 29.2 micrograms/g +/- 56.7 micrograms/g and the median 13.8 micrograms/g (range 0.926-396 micrograms/g). In the other group, comprising 51 persons heavily exposed to nickel, the mean +/- SD was 123 micrograms/g +/- 289 micrograms/g and the median 29.9 micrograms/g (range 1.95-1770 micrograms/g). Both levels were significantly different from the normal nickel concentration in nails (p less than 0.001). The difference between the 2 levels was also significant (p less than 0.001). No correlation between the nickel concentration in fingernails and the duration of exposure could be demonstrated. It was concluded that the higher the nickel level in the fingernails, the greater is the possibility that the person is occupationally exposed to nickel. Nail analysis is suggested as a measure of occupational exposure to nickel.