The potential for clinical HLA class I A and B typing utilizing the polymerase chain reaction combined with sequence-specific oligonucleotide probes (PCR-SSOP) was investigated. Two hundred and ten clinical samples for the HLA-B locus and 100 clinical samples for the HLA-A locus were typed by DNA-based methods and serology. For the HLA-B locus an improved SSOP typing system was developed which involved using HLA-B specific 5' primers and two 3' primers, in separate reactions. Using a panel of 30 digoxigenin-labelled SSOPs, HLA-B types were assigned for all 210 individuals with an improvement in resolution over previously described DNA-based systems and confirming serologically assigned types in all cases except one. In addition, using a single primer pair and a panel of 16 SSOPs, 100 samples were successfully HLA-A typed by PCR-SSOP resolving ambiguous serological types, including HLA-A19 subtypes and A2 homozygosity. In 25 samples, the assigned types were also confirmed by the amplification refractory mutation system (ARMS-PCR). These results indicate that non-urgent clinical HLA-A and -B typing may be performed by PCR-SSOP with a resolution at least equal to that of serology.