Total RNA was isolated from cultured synovial fibroblasts of nine patients with rheumatoid arthritis and two controls (cruciate ligament ruptures). RNA was dot-blotted and hybridized with nine different, cloned cellular or viral oncogene probes. None of the proto-oncogenes showed a significant difference of expression in cultured fibroblasts from patients with rheumatoid arthritis when compared to the expression of control fibroblasts.