The Internet contains scientific information in increasing amounts. It is possible to obtain the latest information, and Web services can easily be maintained and updated. We have set up three Internet services on immunodeficiencies. Immunodeficiency-related mutation infor mation is available in immunodeficiency mutation databases (IDbases). Currently 14 registries are distributed, including information about Bloom syndrome (BLMbase), X-linked agammaglobulinemia (BTKbase), X-linked and autosomal recessive chronic granulomatous diseases (CYBBbase for X-linked CGD, CYBAbase for p22(phox) deficiency, NCF1base for p47(phox) deficiency, NCF2base for p67(phox) deficiency), CD3gamma and CD3epsilon deficiencies (CD3Gbase, CD3Ebase), X-linked hyper-IgM syndrome (CD40Lbase), T-B+ severe combined immunodeficiency (JAK3base), V(D)J recombination defects (RAG1base, RAG2base), X-linked lymphoproliferative syndrome (SH2D1Abase), and ZAP-70 deficiency (ZAP70base). Information on laboratories analysing the genetic defects is collected to IDdiagnostics registry. Due to the rareness of immunodeficiencies there are very few laboratories performing genetic diagnostics. Such laboratories are listed in IDdiagnostics and physicians can use the registry to find a suitable laboratory for their diagnostic needs. Immunodeficiency Resource (IDR) is a comprehensive integrated knowledge base for all the information on immunode ficiencies, including clinical, biochemical, genetic, structural and computational data and analyses. All three services are available at http: //www.uta.fi/imt/bioinfo/.