The incidence of Aeromonas salmonicida as the causative agent of furunculosis in the kidney of anadromous salmonids in Hokkaido were examined. During September to November in 1979 a total of 2,028 fish of four species of salmonids, chum salmon (Oncorhynchus keta), pink salmon (O. gorbuscha), masu salmon (O. masou), and kokanee salmon (O. nerka) were collected for this study at the salmon capture stations in 18 rivers and one lake. In chum salmon, 1,290 fish from 12 rivers were examined and A. salmonicida was isolated from 148 fish. Incidence in each river varied from 0 to 60.5% and was greater in the fish reared for maturation than the others. A. salmonicida was isolated from 66 pink salmon of the 562 fish at 9 rivers. The highest incidence was 36.6 percent at Ichani river. No sign of furunculosis were observed in any chum salmon or pink salmon examined. Other than the salmonids examined, in 116 masu salmon, 60 kokanee salmon and 266 fresh water fish, no A. salmonicida were isolated.