The presence of antinuclear antibodies was determined in female laboratory workers with varying degrees of exposure to blood from patients with systemic lupus erythematosus (SLE). Subjects recruited from SLE research laboratories and a membership roster provided by the American Society for Medical Technology were classified according to self-reported frequency of handling blood from patients with SLE into high and low exposure groups. Employment and medical history were obtained by questionnaire from each study subject and their sera were tested for antibodies to double stranded DNA, single stranded DNA, and synthetic polynucleotide poly(dA-dC).poly(dG-dT) by ELISA. Analysis of the results using an independent t test showed the mean optical density for anti-dsDNA was higher in the high exposure group (mean = 0.010) than in the low exposure group (mean = 0.005, p = 0.016). There were no significant differences found between the 2 groups for anti-ssDNA or anti-poly(dA-dC).poly(dG-dT), but the means for both anti-dsDNA and anti-poly(dA-dC).poly(dG-dT) were higher in the laboratory workers than in an unexposed nonlaboratory group of women (p less than 0.001). Our results are provocative for they lend support to the hypothesis that a transmissible agent capable of causing autoantibody formation may exist in blood from patients with SLE.