Effects of ambient nitrite, NO$_2$$^$-/, at 1, 3, 10 and 30 mg/1, on the changes of plasma nitrite/nitrate and on hepatic drug - metabolizing enzyme activity were examined in the juvenile Israeli carp, Cyprinus carpio. When the fish were exposed to 1 and 3 mg/1 NO$_2$$^$-/, there was an exposure duration-dependent increase in plasma NO$_2$$^$-/ over the 96-hr period reaching 6∼7 fold excess the ambient concentration. In the fish exposed to 10 mg/1, a plateau concentration of less than 2-fold of the environment was attained in 12 hr. With 30 mg/1, however, the maximal plasma NO$_2$$^$-/ was 41.25 mg/1 at 12 hr followed by a gradual decline. There was a concentration-dependent increase in methemoglobin (metHb) level in all NO$_2$$^$-/ -exposed groups and a significant decrease in hematocrit value in 30 mg/l group after 96-hr exposure. Apart from the blunted increase in plasma NO$_2$$^$-/ with higher NO$_2$$^$-/ (10 and 30 mg/1) exposure, the ratio of plasma NO$_3$$^$-/ to NO$_2$$^$-/ was signifirantly higher in these groups compared to 1 and 3 mg/1. The imbalance in the plasma NO$_3$$^$-//NO$_2$$^$-/ at higher NO$_2$$^$-/ exposure suggests a possible accelerated conversion of NO$_2$$^$-/ to NO$_3$$^$-/. Nitrite exposure did not affect the hepatic drug-metabolic activities in juvenile Israeli carp. All these data indicate that disposition of NO$_2$- differ depending upon exposed concentration and that metHb production may not be the exclusive toxic mechanism in carp.