During 1969–71, 41 muscle and 20 liver samples were collected from harbour porpoises (Phocoena phocoena) in the Bay of Fundy region. These tissues were analyzed for total mercury content. Total Hg levels ranged from 0.21 to 1.92 ppm (average 0.75) in muscle tissue of males and from 0.26 to 2.58 ppm(average 1.02) in muscle tissue of females; from 0.89 to 18.30 ppm in liver tissue of males and from 0.55 to 91.30 ppm in liver tissue of females. Averages for the two latter series would be meaningless. A limited number (four muscle and six liver samples) of determinations of the methylated fraction were also made. In the muscle, Hg was virtually 100% methylated; in the liver the methylated fraction varied from 7.4 to 41%, being lowest in livers with highest total Hg.