The effects of pesticides on blood characteristics and histological changes in erythrocytes of the fish species Cyprinus carpio and Puntius ticto were studied. The fishes were exposed to sub lethal concentrations of different chlorinated pesticides namely aldrin, dieldrin, DDT, BHC and chlordane for 10, 20 and 30 d in continuous flow-through test. The LC 50 values were calculated based on acute toxicity tests and the sublethal doses were arrived at for chronic bioassay studies. Results showed an increase in haemoglobin content of both Cyprinus carpio and Puntius ticto in case of aldrin and dieldrin. Haemoglobin content reduced from an initial 13 g/100 ml to 8.07 and 10.15 g/100 ml in case of Cyprinus at the end of ten days exposure to aldrin and dieldrin respectively, and gradually increased to 8.7 g/100 ml and 10.15 g/100 ml after 20 d of exposure. The haemoglobin content after 30 d exposure to aldrin and dieldrin was 10.15 g/100 ml and 11.6 g/100 ml respectively. In case of Puntius ticto, the haemoglobin content in control fishes recorded was 12.8 g/100 ml while in case of fish exposed to aldrin, the haemoglobin content reduced initially on ten days exposure to 10.15 g/100 ml and increased to 11.6 g/100 ml and 13.0 g/100 ml during twenty days and thirty days exposure respectively. This trend was also observed with dieldrin in both the fishes studied. Red blood cells were also counted in case of all the pesticides and exposure periods with respect to Cyprinus carpio and Puntius ticto. Irrespective of the species and pesticide, the RBC counts uniformly showed decreasing trend with the increase in exposure period, while packed cell volume, PCV(%) showed increasing trend with respect to increase in exposure period in case of aldrin and dieldrin in both the fishes. But DDT, BHC and chlordane showed decreasing trend in PCV(%) values with increasing periods of exposure. The effects of pesticides on blood characteristics and histological changes in erythrocytes of the fish species Cyprinus carpio and Puntius ticto were studied. The fishes were exposed to sub lethal concentrations of different chlorinated pesticides to aldrin, dieldrin, DDT, BHC and chlordane for 10, 20 and LC50 values ​​were calculated based on acute toxicity tests and the sublethal doses were arrived at for chronic bioassay studies. Results showed an increase in hemoglobin content of both Cyprinus carpio and Puntius ticto in case of aldrin and dieldrin. Haemoglobin content reduced from an initial 13 g / 100 ml to 8.07 and 10.15 g / 100 ml in case of Cyprinus at the end of ten days exposure to aldrin and dieldrin respectively, and gradually increased to 8.7 g / 100 ml and 10.15 g / 100 ml after 20 d of exposure. The haemoglobin content after 30 d exposure to aldrin and dieldrin was 10.15 g / 100 ml and 11.6 g / 100 ml respectively. In case of Puntiu s ticto, the haemoglobin content in control fishes was 12.8 g / 100 ml while in case of fish exposed to aldrin, the haemoglobin content reduced initially ten days exposure to 10.15 g / 100 ml and increased to 11.6 g / 100 ml and 13.0 This trend was also observed with dieldrin in both the fishes studied. Red blood cells were also counted in case of all the pesticides and exposure periods with respect to Cyprinus carpio and Puntius ticto. Irrespective of the species and pesticide, the RBC counts are showed decreasing trend with the increase in exposure period, while packed cell volume, PCV (%) showed increasing trend with respect to increase in exposure period in case of aldrin and dieldrin in both the fishes . But DDT, BHC and chlordane showed decreasing trend in PCV (%) values ​​with increasing periods of exposure.