A case of PlA1-associated posttransfusion purpura (PTP) is reported, in which a previously sensitized patient developed life-threatening thrombocytopenia, purpura, hematuria, and bronchial bleeding. The patient was transfused with PlA1-negative single-donor apheresis platelets (from four different donors) on four occasions. The first transfusion resulted in a 1-hour posttransfusion increment of 57 times 109 per L. The use of two additional PlA1-negative apheresis platelets provided support for a tracheostomy. Bronchial bleeding leading to respiratory arrest was controlled with a fourth transfusion. All PlA1-negative platelet transfusions resulted in transient increases in the patient's platelet count. This is the first reported case of repeated, transiently effective transfusion of PlA1-negative platelets demonstrated during the acute phase of thrombocytopenia.