Nicarbazin, a complex of two compounds, 4,4'-dinitrocarbanilide (DNC) and 4,6-dimethyl-2-pyrimidinol (HDP) is an effective drug for preventing intestinal and caecal coccidiosis in poultry. It is used for prevention rather than the treatment of disease. Nicarbazin was the first agent with “broad‐spectrum” activity against Eimeria spp. of chickens. Nicarbazin is used as a single agent or in combination with polyether antibiotics (narasin, or maduramicin), roxarsone, or antibiotics (lincomycin, bacitracin, flavomycin) for prevention and control of coccidiosis caused by Eimeria spp. (all relevant species) in broiler chickens. Nicarbazin can cause increased sensitivity to heat stress, which may result in growth depression and even mortality in broilers; death may be due to cell degeneration processes in liver and kidneys; at the recommended dose, the drug causes occasionally toxic effects in laying hens like reduced hatchability and interruption of egg-laying. Nicarbazin interferes with the formation of the vitelline membrane, separating the egg yolk and egg white. The exact mode of action is unknown, although it is thought nicarbazin interferes with cholesterol metabolism in the formation of the membrane.