The two-allele NcoI Restriction Fragment Length Polymorphism (RFLP) of the TNF alpha region yielding bands of 5.5 and 10.5 kb was investigated in patients with systemic lupus erythematosus (SLE), pauciarticular juvenile rheumatoid arthritis (P-JRA), rheumatoid arthritis (RA) and primary Sjögren's syndrome (pSS). In all four disease, we found a decreased frequency of the 10.5 kb allele which, however, was significant only in the SLE group. In all conditions except RA, the frequency of the 5.5 kb fragment was increased. In pSS and SLE, the frequency of HLA-B8 was increased in 5.5 kb fragment positive patients compared with corresponding controls and thus, the increase of this band and the decrease of the 10.5 kb band may be secondary to HLA-B8 associations owing to strong positive linkage disequilibrium between HLA-B8 and the 5.5 kb band.