Stored serum specimens collected in connection with a community-oriented epidemiologic study were available from 30 subjects who later developed seropositive rheumatoid arthritis. In 9 of these pre-rheumatoid specimens, the Rose-Waaler test result was positive, and in 16, the latex fixation test was positive. Two-thirds of the samples were positive when the interval between taking the blood specimen and onset of the disease was less than 4 years, and one-third were positive when the interval was greater than or equal to 4 years. The occurrence of rheumatoid factor preceded the onset of clinical disease more often in males than in females.