BACKGROUND: Uterine leiomyoma is the most common pelvic tumor, occurring in 20-25% of women in reproductive age. Gonadotropin releasing hormone agonist (GnRHa) has been reognized as a temporary medical management for this disorder. The etiology of these tumors is unknown but it has been shown that the insulin-like growth factors (IGF-I, IGF-II) are promoters of growth in nongynecologic tumors. Several recent studies have suggested the possible role of IGFs in human leiomyoma growth. The IGF binding proteins (IGFBPs) are believed to modulate actions of IGF and to have IGF-independent actions. The purpose of this study was to evaluate the type of IGF and IGFBP which may be involved in leiomyoma growth and to investigate a possible IGF related mechanism of action of GnRHa. METHOD: The IGFs and IGFBPs were measured by double antibody radioimmunoassay, western ligand blot and immunoprecipitation in the tissue cytosols of normal uterine myometria (n=15), nontumorous myometria adjacent to a leiomyoma and leiomyoma from patients nontreated (n=15) and treated (n=10) with GnRHa. RESULTS: The mean IGF-I and IGF-II level were significantly higher in leiomyoma from untreated patients than in the adjacent myometrium and normal myometrium but no significant differences in these IGF levels between normal myometrium and adjacent myometrium were noted. The IGFBP-2, IGFBP-3 and 26kDa IGFBP were detected variably but IGFBP-4 was consistently present in all tissues. There were no significant differences in the relative intensity for IGFBP-4 and the frequency of IGFBPs between leiomyoma, adjacent myometrium and normal myometrium from untreated patients. The IGF-I, IGF-II levels and the relative intensity of IGFBP-4 in leiomyoma from GnRHa-treated patients were significantly lower than those in untreated patients, but these levels in the adjacent myometrium were comparable. The frequency of each IGFBP in leiomyoma and the adjacent myornetrium from GnRHa-treated patients did not significantly differ from untreated patients. CONCLUSION: Both IGF-I and IGF-II are involved in the growth of leiomyoma and GnRHa may in part act to decrease size of leiomyoma by regulating the local levels of IGF-I, IGF-II and IGFBP-4.