Mercury and 12 clinical chemical determinations were done on the blood samples of 1,555 dentists. The dental practice characteristics of each participant were determined by questionnaires. Seventy-seven percent of all the dentists displayed blood mercury values in the range 0 to 10 ng/ml. The mean for all dentists was 8.2 ng Hg/ml blood. The means for general dentists and specialists were 8.8 and 6.3 ng Hg/ml blood, respectively. Overall, no significant correlations were found in a comparison of blood mercury levels with clinical chemical data and with dental practice characteristics. However, general practitioners with higher blood mercury values tended to show dental practice characteristics that were conducive to producing the higher values found. The data indicate that dentists in the United States, as a group, practice good mercury hygiene.