The prevalence of autoantibodies during pregnancy was studied. Sera from 568 women (203 pregnant and 365 non-pregnant) were tested for autoantibodies to double-stranded DNA, cardiolipin and extractable cellular antigens. Nineteen out of 203 pregnant women (9.4%) had at least one autoantibody against double-stranded DNA or cardiolipin, mainly of the IgM class. The non-pregnant control group had significantly higher incidence of autoantibodies (17.8%; chi 2 = 7.39, P < 0.01). Sixty-six out of 568 women had had spontaneous abortions in their past medical history, but there was no correlation between them and the presence of anticardiolipin antibodies. Two of the non-pregnant women had anti-Ro(SSA) antibodies. These findings suggest that (a) the prevalence of autoantibodies decreases during pregnancy; and (b) the presence of anticardiolipin antibodies in healthy pregnant women does not correlate with any pregnancy-related complications. However, our results indicated that autoimmunity is a rather common disorder in healthy women.