Human leukocyte antigen (HLA) genotyping is routinely performed prior to organ transplantation using peripheral blood leukocyte-derived DNA. In addition, polymerase chain reaction (PCR)-based methods have permitted HLA genotyping using DNA extracted from formalin-fixed and paraffin-embedded tissue, with proven applications in HLA-disease association studies and surgical biopsy identification. The utility of current techniques may be limited by the poor yield of intact DNA from such paraffin biopsies. This paper describes a new nested PCR-based HLA class II genotyping method which reliably detects HLA DRB alleles within DNA extracted from even extremely small paraffin biopsies. This method comprises initial PCR amplification of exon II sequences of the HLA DRB1, 3, 4, and 5 genes using generic PCR primers. Identification of the HLA DRB1 alleles and detection of the DRB3, 4, and 5 genes is then performed using a series of separate individual second-round PCR reactions, each of which contains PCR primer pairs detecting a single HLA DRB allele or group of alleles (PCR-SSP). The ability of this method to detect 19 individual HLA DRB1 alleles or groups of alleles, covering all common DRB1 specificities, was confirmed via concordant results when compared with 'direct' (single amplification step) PCR-SSP analysis of one cell line-derived and nine peripheral blood-derived DNA samples, and with five DNA samples extracted from paraffin biopsies. The technique was then successfully applied to 11 further paraffin biopsy-derived DNA samples, of which ten were untypable by 'direct' PCR-SSP analysis, from five cases in which doubt existed as to the individual origin of the tissues.