We report here follow-up data on subjects who were examined in two surveys conducted by the United States Center for Health Statistics at an interval of 8 years. The first survey was the 1st National Health and Nutrition Examination Survey (NHANES-1), and the second conducted 8 years later was the National Health and Nutrition Epidemiologic Follow-up Study (NHEFS). From an original sample of 3023 subjects, 153 were known to be deceased, leaving a potential sample of 2870 cases, of whom 2341 were ultimately examined in the NHEFS. The definition of pain used in the NHANES-1 survey identified 15% of the subjects as suffering from persistent pain. Using a different pain definition, in the NHEFS, the frequency of subjects with chronic pain was 32.8%. Applying this second definition, the percentage of subjects with chronic pain in the NHANES-1 had risen from 15 to 20.2. Some subjects (32.5%) who originally had chronic pain were free from pain at the time of follow-up; 59% of the subjects with chronic pain on follow-up did not have it initially. As found originally in the NHANES-1, the group with chronic pain at the NHEFS comprised significantly more females, older people, and people with lower income. On logistic regression analysis the strongest relationship found at the NHEFS between the variables examined was between chronic pain and depression.(ABSTRACT TRUNCATED AT 250 WORDS)