Analysis of caribou fecal samples from 4 distinct caribou wintering areas revealed expected relative percentage use of lichens among the areas. Additional uses of fecal analysis include identification of most major plant groups in the diet, detection of trends in condition in Rangifer winter range, and substantiation of estimated winter diets of free-ranging Rangifer using captive Rangifer hand-fed the estimated diets. An index to relative winter diet quality can be developed using both fecal analysis and forage nutrient analysis. Nutrient analysis of fecal samples can provide indices to seasonal diet quality and nutrient flow. Fecal analysis inadequately estimate Rangifer diets by overestimating proportions of mosses and, at times, evergreen shrubs. Mushrooms and many green 'forbs' (excluding Equisetum spp.) are underestimated or not detected. These over- and underestimates require the investigator to adjust the proportions of other plant groups present, particularly lichens. Correction factors can become arbitrary unless additional information is obtained. Additional information can include data on actual diet composition or data from feeding trials. Development of correction factors through feeding trials is useful only on case-by-case basis where estimates of individual diets require substantiation, and mushrooms and green forbs are not large proportions of suspected diets.