We applied a polymerase chain reaction-sequence specific primer (PCR-SSP) method developed by other researchers to study 4 families of newborns with neonatal alloimmune thrombocytopenia (NAITP) in which serology had provided inconclusive human platelet antigen (HPA) typing data. This method allowed for the identification of the newborn HPAs which were incompatible with their respective mothers. They were HPA-2b, -1b, -3a, and -5b. This PCR-SSP is a useful tool for improving the ability to identify the incompatible HPA in NAITP.