WE report here diseases of reef corals that seem to be associated with bacterial infection. On reefs around Bermuda, where our field work was carried out in the summer of 1973, the most commonly affected species are the brain corals Diploria labyrintheformis and D. strigosa (Fig. 1). We believe that this is the first unequivocal report of a coral disease and our observations suggest that diseases may be important agents of coral death. (There are some indications that others have seen diseased corals1,2.)