Effects of ambient nitrite, NO₂^-, at 1, 3, 10 and 30 mg/l, on the changes of plasma nitrite/nitrate and on hepatic drug-metabolizing enzyme activity were examined in the juvenile Israeli carp, Cyprinus carpio. When the fish were exposed to 1 and 3 mg/l NO₃^-, there was an exposure duration-dependent increase in plasma NO₂^- over the 96-hr period reaching 6~7 fold excess the ambient concentration. In the fjsh exposed to 10 mg/l, a plateau concentration of less than 2-fold of the environment was attained in 12hr. With 30 mg/l, however, the maximal plasma NO₂^- was 41.25 mg/l at 12hr followed by a gradual decline. There was a concentration-dependent increase in methemoglobin(metHb) level in an N0₂^--exposed groups and a significant decrease in hematocrit value in 30mg/l group after 96-hr exposure. Apart from the blunted increase in plasma NO₂^- with higher NO₂^-(10 and 30mg/l) exposure, the ratio of plasma NO₃^- to NO₂^- was significantly higher in these groups compared to 1 and 3 mg/l. The imbalance in the plasma NO₃^-/NO₂^- at higher NO₂^- exposure suggests a possible accelerated conversion of NO₂^- to NO₃^-. Nitrite exposure did not affect the hepatic drugmetabolic activitjes in juvenile Israeli carp. All these data indicate that disposition of NO₂^- differ dependjng upon exposed concentration and that metHb production may not be the exclusive toxic mechanism in carp.