This invention relates to a group of substituted pteridine derivatives, their pharmaceutically acceptable salts, N-oxides, solvates, dihydro- and tetrahydro-derivatives, and enantiomers, possessing unexpectedly desirable pharmaceutical properties, in particular which are highly active immunosuppressive agents, and as such are useful in the treatment in transplant rejection and/or in the treatment of certain inflammatory diseases. These derivatives are also useful in preventing or treating cardiovascular disorders, allergic conditions, disorders of the central nervous system, TNF-.alpha. related disorders, viral diseases, inflammatory bowel diseases and cell proliferative disorders.