Recent reports strongly suggest an association between a laboratory picture of autoimmunity in the absence of clinical signs and symptoms and the recurrence of spontaneous pregnancy loss. This association seems particularly strong when circulating lupus anticoagulant is present and has therefore been called the circulating lupus anticoagulant syndrome. We present four patients with this syndrome who in addition to the asymptomatic autoimmune laboratory picture were also found to exhibit a distinct IgM gammopathy. In view of earlier reports that implicated IgM in poor pregnancy outcome, particularly in association with systemic lupus erythematosus, it is suggested that all patients with circulating lupus anticoagulant syndrome be evaluated for an IgM gammopathy. A fraction of IgM may be detrimental to development and growth of the normal fetal placental unit and may thus be implicated in repeated early pregnancy loss.