Dopamine　receptor　agonists　(DAs)　can　reduce　hormone　release　and　tumor　mass　in　the　majority　of　prolactinomas,　whereas　such　effects　are　controversial　in　clinically　nonfunctioning　pituitary　adenomas　(NFPAs).　Whether　expression　of　dopamine　2　receptor　(D2R)　is　different　in　subgroups　of　NFPAs　has　not　been　fully　elucidated.　We　assessed　and　compared　D2R　subtype　(long:　D2L　and　short:　D2S)　mRNA　levels　in　subgroups　of　NFPAs　by　real-time　reverse　transcriptase　polymerase　chain　reaction　(RT-PCR).　For　both　D2L　and　D2S　mRNA,　there　were　no　significant　differences　among　them.　Only　21.6%　of　NFPAs　showed　relatively　high　D2R　mRNA　levels;　furthermore,　histopathological　subtypes　of　those　cases　with　relatively　high　D2R　expression　were　gonadotropinomas　and　null-cell　adenomas.　These　data　suggest　that　DAs　are　effective　only　for　a　small　proportion　of　NFPAs,　and　relatively　high　D2R　expression　may　more　possibly　happen　to　a　subset　of　gonadotropinomas　and　null-cell　adenomas.