The primary objective of this study was to suggest a possible mechanism of action of luteinizing hormone-releasing hormone agonist (LHRHa) on fibroids. This was performed by investigating insulin-like growth factor (IGF)-I, IGF-II and IGF binding protein (IGFBP)-1, -2 and -3 mRNA expression in uterine fibroids from women rendered hypo-oestrogenic by LHRHa, using Northern blot analysis. Nine women with fibroids, who were rendered hypo-oestrogenic from at least 4 months pretreatment with LHRHa therapy prior to undergoing myomectomy were investigated. Our results showed that IGF-I, IGF-II, IGFBP-2 and -3 mRNAs were expressed in uterine fibroids, and that IGFBP-1 mRNA or protein was not detected in fibroids. Western ligand blotting showed the presence of IGFBP-2 and -3 proteins, and when compared with a group of women with fibroids not treated with LHRHa (B.J. Vollenhoven et al., 1993, J. Clin. Endocrinol. Metab., 76, 1106-1110) we found that there was no difference in the relative abundance for each of the factors between the two groups of women. Therefore, LHRHa act to decrease fibroid size via induction of a hypo-oestrogenic state rather than by changes in the IGFs and their IGFBPs.