Immunological abnormalities seen in relatives of patients with autoimmune disorders can be useful in understanding the pathogenesis of the disease since, unlike in patients, they cannot result from the disease process or drug treatment. In this article we present a brief overview of our studies of the basic immunological status of close relatives of SLE patients. We looked at blood levels of IgG, IgM and antibodies to double-stranded DNA, as well as at NK cell numbers and cytotoxic activity and the levels of NKT, B and T cells. As many as 60% of relatives showed one or more abnormalities in these assays. Most notably there were increased levels of IgG in male and female relatives and a reduction of IgM in females. IgG correlated inversely with NKT cell numbers adding strength to the concept that the presence of IgG autoantibodies in patients is due to impaired regulation by NKT cells. IgM, on the other hand, correlated inversely with NK cells which may thus have a role in bringing about the reduced IgM seen in some patients. Immunological abnormalities were found to be more often associated with parents and offspring of patients than with their siblings, pointing to the involvement of environmental or epigenetic influences in lupus pathogenesis.