To use proteomic techniques, including two-dimensional electrophoresis (2DE), Western blot, and mass spectrometry, to screen and identify proteins that were expressed differently in patients with uterine leiomyoma versus normal myometrium.First, identify proteins important for leiomyogenesis by comparing protein expression in leiomyoma and normal myometrium. Second, examine the expression level of selected proteins on a larger panel of leiomyomas.Academic research laboratory.Consenting premenopausal patients scheduled to undergo hysterectomy for symptomatic uterine leiomyomas.Paired samples of leiomyoma and adjacent myometrium were obtained and submitted to 2DE, mass spectrometry, Western blot, reverse transcription polymerase chain reaction (RT-PCR), and immunohistochemistry.Protein expression.A comparison of protein patterns revealed 37 protein spots significantly changed, with 10 protein spots with concordantly increased and 27 protein spots with concordantly decreased intensity in leiomyoma compared with normal myometrium. Ten of these proteins were identified by tandem mass spectrometry. Interestingly, one of the proteins, which exhibited a marked down-regulation in leiomyoma tissues, was the recently identified highly conserved cellular protein 14-3-3-gamma. The reduction of the 14-3-3 gamma in leiomyoma tissues was confirmed by comparative immunoblotting (n = 25) and RT-PCR (n = 25) as well as by immunohistochemistry (n = 35) of individual-matched neoplastic and normal myometrium tissue specimens.The consistency of 14-3-3 gamma reduction in uterine leiomyoma suggests that 14-3-3 protein may play a role in the origin or growth of leiomyoma.