TNFa, TNFb and TNFc microsatellites were analyzed in 102 SLE patients recruited from a defined area in Southern Sweden. Furthermore we studied 27 SLE patients belonging to 10 multiplex families in which a majority of the members were living within the same area in Southern Sweden. As a control population 98 healthy blood donors from the same region was used. The TNFa2 allele was found more often in the SLE patients (48%) than in the normal controls (33%) (P < 0.01). A low frequency of the TNFa4 allele (10%) vs 16% in controls was observed. The family study showed that the TNFabc haplotype 2-3-1 was more common in SLE associated haplotypes than in non-SLE haplotypes (P < 0.001). The 2-3-1 haplotype was associated with the extended haplotype MHC haplotype [HLA-B8,SC01,DR17]. The results suggest that TNF haplotypes do not constitute special markers of susceptibility to SLE but reflect the increased frequencies of specific intact haplotypes already known to be associated with the disease.