An Expert Panel on Vitamin A Nutriture assessed serum vitamin A values and related data collected during the first and second National Health and Nutrition Examination Surveys (NHANES I and NHANES II) and the southwest component of the Hispanic Health and Nutrition Examination Survey (SW HHANES). The appropriateness of the analytical methodologies and adequacy of the quality-control procedures used to obtain the serum vitamin A values were evaluated. Age-specific guidelines for the interpretation of serum vitamin A values in selected low ranges (less than 20, 20-24 and 25-29 micrograms/dl) were developed, and estimates of the prevalence of serum vitamin A values in these ranges were presented for each of the three surveys.