The prevalence of biochemical and immunological abnormalities was studied in a group of 256 patients with rheumatoid arthritis (104 coloureds, 100 whites and 52 blacks). The most common biochemical abnormalities detected were a reduction in the serum creatinine value (43.4%), raised globulins (39.7%), raised serum alkaline phosphatase level (42.3%), reduction in serum albumin value (8.1%), a mild rise in serum creatinine value (6.6%), and a raised serum gamma-glutamyltranspeptidase (GGT) level (6.5%). The prevalence of a rise in the GGT was less frequent than reported in other published studies. The immunological abnormalities noted were a positive rheumatoid factor (78.9%), positive anti-nuclear factor (36%), raised serum IgG (43.3%) and IgA (10.5%) values, positive smooth-muscle antibody (12.5%) and elevated double-stranded anti-DNA antibody levels (2.3%). Inter-group comparisons showed that the serum IgG and IgA and total globulins were significantly higher in blacks and coloureds than whites; these findings may be related to a higher prevalence of malnutrition and infection in childhood in these communities. There were no significant inter-group differences that could be attributed to rheumatoid arthritis.