This invention relates to a group of trisubstituted and tetrasubstituted pteridine derivatives, having the formula: ##STR00001## wherein X represents an oxygen atom or a group with the formula NZ and wherein: R.sub.1 C.sub.1-7 alkyl or arylalkyl; Z is a group independently defined as R.sub.1 or the group NZ together with R.sub.1 is an optionally substituted heterocyclic group containing at least one nitrogen atom; R.sub.2 is amino or acylamino; R.sub.4 is an atom or a group selected from the group consisting of hydrogen; C.sub.1-7 alkyl; and C.sub.1-7 alkoxy; and R.sub.3 is an atom or a group selected from the group consisting of aryl optionally substituted with one or more substituents selected from the group consisting of halogen, C.sub.1-7 alkyl, and C.sub.1-7 alkoxy, their pharmaceutically acceptable salts, and enantiomers, possessing unexpectedly desirable pharmaceutical properties, in particular which are highly active immunosuppressive agents, and being useful in the treatment in transplant rejection, certain inflammatory diseases, cardiovascular disorders, allergic conditions, disorders of the central nervous system and cell proliferative disorders.