Total Hbs were compared for affinity to 02 among the 2 subspecies of the Japanese char, Salvelinus leucomaenis pluvius, called 'Nikkoiwana' and S. l. imbrius, called 'Gogi'. At pH7.8, 0_2 saturation curve was a little steeper for Nikkoiwana than for Gogi, but the P_<50> value was almost at the same level (13 and 12torr, respectively). At pH7.O, however, 0_2 saturation curve was slightly steeper for Gogi than for Nikkoiwana, and the P_<50> value was about 78 and 92torr, respectively. This suggests the differences in dissolved oxygen concentration between the water environments to which the two subspecies had adapted.