The clinical history, deposition of IgG, IgM, IgA, C3, C4 and properdin at the dermal-epidermal junction (DEJ) of clinically normal skin, serum ANA, DNA-binding, C3, C4, Factor B, and properdin were compared in 27 systemic lupus erythematosus (SLE) probands, 21 first-degree household contact relatives (FDHCR), 19 first-degree nonhousehold contact relatives (FDNHCR), 15 spouses, 26 controls, and 16 chronic discoid lungs lupus erythematosus patients. Female consanguineous relatives of SLE patients had a higher incidence of rheumatic symptoms than male relatives (P less than 0.01). Female FDHCR and male spouses had a higher incidence of protein deposition at the DEJ than sex-matched controls (P = 0.026 and 0.0028). The incidence of protein deposition at the DEJ in FDNHCR did not differ from sex-matched controls. ANA titers of the consanguineous relatives were significantly higher than those of the spouses or sex-matched controls irrespective of household contact with their proband. The observation of protein deposition at the DEJ in normal appearing skin of FDHCR and spouses suggests the importance of environmental factors, whereas the elevations of ANA titers in consanguineous relatives suggests the importance of genetic factors in the pathogenesis of SLE.