1. Review of the evidence of the Irish Nutrition Survey concerning a market rise in the incidence of rickets in Dublin in 1942 concludes that a rise in the extraction rate of the national flour from 70 to 100% was principally responsible. 2. This rise and subsequent decrease in incidence as the extraction rate of flour was reduced is not explained by changes in the proportion of children protected by vitamin D supplements or by small changes in dietary vitamin D intake. 3. The evidence suggests that nutritional rickets in man cannot be explained on the basis of deficient vitamin D intake alone, whether derived from diet or u.v. radiation.