The effects of exposure to one-third and one-fifth sublethal concentrations (0.106 and 0.064 mg/L) of sodium cyanide on protein metabolism on freshwater carp, Labeo rohita, was studied. Three functionally different tissues, namely, the liver, muscle, and gills, were studied after 5, 10, and 15 days. Exposures produced marked changes in protein metabolic profile in all tissues studied. These changes were more pronounced in the one-third sublethal concentration, suggesting a cumulative action of toxicant. This investigation revealed that the total, structural, and soluble proteins and urea content in all the three tissues were decreased, whereas free amino acids, ammonia, and enzyme activity (i.e., protease, alanine aminotransferase, and aspartate aminotransferase) exhibited elevated levels at both sublethal concentrations. Variation in protein metabolism in the fish, induced by sodium cyanide, demonstrated its toxic effects on cellular metabolism, thereby leading to impaired protein synthetic machinery. The results of the present study indicate that a mechanism of impaired energy transformation has direct action on the fish, L. rohita, and its impact is clearly evident from the change in the nutritional content of the fish.