The activities of the Children's Hospital of Pittsburgh Histocompatibility Center can be classified under three major categories: 1) the repository service; 2) the molecular typing service; and 3) the research activities aimed at improving the technical support on which the previous two services are working. This year in the Repository, where blood samples from volunteers as bone marrow donors are collected from more than 125 recruiting centers nationwide, 165,203 samples were processed. We stored 495,609 vials in three sets of freezers (one sample per donor each freezer), while 216,712 were sent out to other Typing Laboratories for molecular HLA typings. In our laboratories, 10,626 typings were performed with a very high Q.C. standard, as monitored by National Marrow Donor Program. Our Center's research branch synthesized all the oligonucleotides to be used as PCR primers or labelled probes to perform molecular HLA typing. DNA sequencing was also performed when hybridization results were not optimal. Alternatives for storing blood samples (e.g., blood spots on filter paper) or for enhancing typing capabilities (e.g., microchip technology to expedite PCR procedures) were successfully implemented or improved to the point of justifying their future implementation.