AbstractIn the present work, histological changes in the gill, liver, kidney and intestine ofNotopterus notopterus, induced by pulp waste, paper waste and mixed pulp and paper waste, have been studied both at sublethal and lethal concentrations.The pulp waste produces much more histological changes both at sublethal and lethal concentrations in the gill, liver, kidney and intestine as compared to paper waste and mixed pulp and paper waste. The changes are much more remarkable in the case of sublethal concentration, as compared to a lethal concentration.In a sublethal concentration, the localized necrosis, atrophy and partial and total liquefaction of epithelial cells, pilaster cells, mucous cells of the gill, hepatic cells of the liver, mesenchymatous cells, renal tubule cells and Bowman's capsule of the kidney, mucosal and submucosal cells and blood vessels of intestine have been observed.In lethal concentration, the changes are much more marked in the gill, as compared to the liver, kidney and intestine.The histological changes, produced in the different types of cells and in the tissue as a whole, can be correlated with the different chemical components present in the pulp waste, paper waste and mixed pulp and paper waste.