Virulent Pediococcus homari, the etiological agent of gaffkemia, a disease enzootic in Atlantic lobsters (genus Homarus), was isolated from two sites in Anaheim Bay, Calif. The concentration of P. homari was in the order of 1–10 bacteria per ml of sample. This is the first known report of free-living P. homari in the Pacific; the bacterium was previously reported to exist in infected decapod Crustaceae and sediments from the Atlantic. Introduction of P. homari may have occurred through transport of infected Homarus americanus (Atlantic lobster), or by discharge of water in contact with them.