Recurrent spontaneous abortion (greater than or equal to 3 spontaneous miscarriages) represents an entity defined by negative criteria (absence of anatomical, hormonal, autoimmune and chromosomal abnormalities). The immune hypothesis is corroborated by the successes (greater than or equal to 80 %) of specific (paternal leucocytes) or non-specific (intravenous gammaglobulins) immunotherapeutic trials. Studies on the mechanisms of action of those two methods will afford information on the pathogenesis of this condition.