A system, accessible via internet, has been developed to support the Spanish Registry of Cord Blood Transplants (RETSCU). The system includes a database of clinical results directly accessible by transplant centers (TCs) and cord blood banks (CBBs) (restricted to own cases regarding primary data and unrestricted regarding statistics derived from validated data) and gives open access to Web pages containing results approved for publication. It also includes internal mail for two-way and broadcast messages. Patients' data are essentially those included in Eurocord forms. Additional features of the system are: confidentiality; inalterability of validated primary data; identifiability of data sources. The Unix central computer is accessible via the WWW. For security, data transmission is encrypted and passwords are required for access. Copies are regularly updated. Data can be loaded from CBBs and TCs. The procedure for creating and updating records is user-friendly, with the possibility of errors being minimized by extensive automated checks. Validation of patients' records by a manager is required before making data available for general statistical analysis. TCs and CBBs may retrieve data on their own cases, regardless of validation, as individual records or in tables directly transferable to common statistical programs. Statistical analysis may be done on validated data from all the patients in the Registry or from groups selected according to HLA compatibility and disease, type of transplant (related/unrelated), or protocol. Several similarly designed and managed national/regional Registries might be networked and their data integrated into a multinational Registry. Our system would require some additional developments to be used in this way.