Urinary mercury (U-Hg) and plasma mercury (P-Hg) levels were higher in 244 dental personnel than in 81 matched referents (U-Hg: 1.8 and 1.1 mumol/mol creatinine, respectively; p less than .001; P-Hg: 6.7 and 6.2 nmol/l, respectively; p = .03). The amalgam in the mouth influenced mercury levels in whole blood (B-Hg), plasma, and urine. The association was nonlinear: the more amalgam, the larger the relative increase in mercury levels. The number of amalgam surfaces accounted for more of the variance in blood and urine mercury levels than did the number of fillings (e.g., U-Hg: 44% and 36%, respectively). The estimated increases in mercury level with rising amalgam load were 3.0%, 2.0%, and 0.8% per filled surface for U-Hg, P-Hg, and B-Hg, respectively (p less than .0001 in all cases). The impact of occupational exposure on U-Hg in the dental personnel corresponded to approximately 19 amalgam surfaces. Ceramo metallic restorations were associated with higher (31%) U-Hg.