For several years, rapid tissue tests have been used in the field to evaluate plant nutritional status and to diagnose deficiencies. But they have been used only incidentally to make fertilizer recommendations, or to evaluate a fertilizer program, partly because they have lacked the accuracy of laboratory analysis. Research has revealed definite and consistent relationships between plant nutrient level and plant health. However, few crops are routinely tested to determine plant nutritional needs, because fertilizer has been plentiful and relatively low in cost, and because results from laboratory analyses are often delayed. Rapid tissue tests conducted in the field could overcome the problem of delay. By providing information about nutrients needed for a particular crop in any given field, the tests also enable growers to more fully utilize increasingly costly and limited fertilizer resources. In the field investigations reported here, a rapid tissue testing procedure (developed by R. H. Bray in 1945 at the University of Illinois) was found useful as a guide for evaluation of the nitrogen nutritional status of corn and sorghum. Resulting guidelines are given here for recommending application rates for nitrogen fertilization and for evaluation at the end of the growing season.