Human neutrophil antigen-4a (HNA-4a) is a high-frequency (99% in the USA) neutrophil antigen, which has recently been linked to a case of alloimmune neonatal neutropenia. We have devised a new polymerase chain reaction sequence-specific primer (PCR-SSP) method to assess HNA-4a genotype, and used it to determine the HNA-4a gene frequencies in an Australian population. The gene frequency was found to be 0.906, which is the same as in the American population. The PCR-SSP genotyping method perfectly correlates with serological phenotyping and is efficient for screening large numbers of samples.