The biological diagnosis of virus and virus-like diseases of stone fruit trees was briefly discussed. Mechanical transmission and graft inoculation were separately exposed with a special reference to certification programs. Indexing facilities and the activities conducted in the framework of certification were also described. A list of virus and virus-like diseases of stone fruits and their main indicators were given. Finally, it was stressed that biological assays in general and woody indexing in particular still remain a compulsory tool for sanitary selection and certification programs.