Thrombocytopenia has been documented infrequently in association with congenital heart block or lupus dermatitis in the neonatal lupus erythematosus syndrome. We report the cases of two infants with transient neonatal thrombocytopenia born to mothers with connective-tissue disease. Both mother/infant pairs were Ro(SS-A) antibody positive. Although the finding of neonatal thrombocytopenia in the presence of maternal connective-tissue disease suggests an autoimmune thrombocytopenia, platelet antibody studies were negative in both mother/infant pairs. We have found the Ro (SS-A) antibody with increased frequency in idiopathic thrombocytopenic purpura and thrombocytopenia associated with Sjögren's syndrome, but the nature of the association is unknown. We suggest that thrombocytopenia in our patients is a manifestation of the neonatal lupus erythematosus syndrome. This syndrome should be included in the differential diagnosis of neonatal thrombocytopenia.