Oncopsis alni leafhoppers were captured on field-grown Alnus glutinosa that were infected by alder yellows phytoplasma. This pathogen is indistinguishable by RFLP of ribosomal and non-ribosomal DNA fragments from a phytoplasma associated with grapevine yellows in the same region. PCR tests revealed that approximately 11 % of the insects carried the pathogen. Their ability to inoculate grapevine was studied by transmission experiments. Three of 88 test plants developed typical symptoms of grapevine yellows, and the respective phytoplasma could be detected in symptomatic plants by PCR. Thus, O. alni was identified as a vector of a grapevine yellows of the elm yellows group.