The importance of immunological parameters such as anti-globulins, anti-RANA and circulating immune complexes in rheumatoid arthritis (RA) has been studied by examining patients with early disease who are attending general practitioner clinics with joint pains for the first time. Anti-RANA, and IgG and IgM anti-globulins were detectable in the serum at the earliest time we were able to examine the patients. The anti-globulins had specificity for both rabbit and human IgG from the outset. Immune complexes were similarly raised in early disease. From these patients with early joint pains we were able to predict, by means of multivariant discriminant analysis of the laboratory data obtained from the first serum sample, between those who would develop into patients with classical or definite RA at 1 year and those who would have non-inflammatory joint disease.