The effects of chronic administration of two organophosphorus insecticides, parathion and malathion on the growth rate, ascorbic acid metabolism and some other nutritional and physiological parameters in rats were studied. Both parathion and malathion toxicity retarded the growth rate of rats. Inhibition of brain acetylcholinesterase was taken as an index of organophosphorus insecticide toxicity. Haemoglobin concentration of blood and organ weights were not affected under the toxic conditions. Parathion and malathion administration stimulated the activity of L-gulonolactone oxidase along with a simultaneous increase in the tissue storage and urinary excretion of vitamin C. The activities of other enzymes of ascorbic acid metabolism, dehydroascorbatase, uronolactonase, and L-gulonate dehydrogenase and decarboxylase were altered under the experimental conditions. Only minor histological changes of the liver and kidney tissues were noted under parathion and malathion toxicities. Excess intake of vitamin C under the toxic conditions was found to be very effective in counteracting the growth retardation and also the alterations produced by parathion and malathion both at the enzymatic and histological levels.