The acute and chronic effects of 2,4-Diamin, which is a widely used herbicide, were investigated in freshwater fish, Cyprinus carpio (L.). The fish were exposed to 50 and 80 ppm sublethal concentrations of the herbicide for 1, 2, 3, 4, 15, and 30 days. Various changes in protein and carbohydrate metabolisms in the serum, muscle and liver tissues were determined photometrically. Both concentrations of 2,4-Diamin inhibited glutamate-oxaloacetate transaminase activity in 30-days treatment and glutamate-pyruvate transaminase activity on 2-days treatment in the serum. The results showed an increase in lactate dehydrogenase activity at 1-day exposure to 50 ppm 2,4-Diamin, while it was at control level on the other days. Then was no change in all periods after exposure to 80 ppm 2,4-Diamin concentration. Exposure to herbicide did not alter the activities of alkaline phosphatase and acid phosphatase. The effect of herbicide caused an increase in protein lever in the liver in order to compensate for any possible protein loss. There was a reduction in muscle and liver glycogen levels, but serum glucose level was higher in herbicide-exposed fish than in control fish. The results in the carbohydrate metabolism suggest that an increase in the rate of glycogenolysis in the tissues of fish could be because of the stress caused by the herbicide. (C) 1999 Elsevier Science Ltd. All rights reserved.