Androgens are essential for normal prostatic and testicular function. However, paracrine and/or autocrine actions of a number of growth factors have been implicated in the function of these tissues. A recent addition to the fibroblast growth factor family, the so called androgen-induced growth factor (AIGF) or fibroblast growth factor-8 (FGF-8), has been proposed to be under strict androgen regulation and induction in the mouse mammary carcinoma cell line SC3. FGF-8, therefore, may have a local role in the prostate, which is known to be an androgen-responsive organ. This study reports, for the first time, the presence of FGF-8 mRNA in normal adult rat tissues (heart, brain, lung, kidney, testis, prostate and ovary), using an optimised reverse transcription and nested polymerase chain reaction (RT-PCR) procedure, although androgen-dependent FGF-8 expression was not demonstrated in these adult tissues. Consistent with the oncogenic characteristics of FGF-8, the corresponding mRNA was detected in the human prostate tumour cell lines LNCaP and DU145. Because the DU145 cell line is known to be androgen-independent, and the expression of FGF-8 mRNA in cultured LNCaP cells also occurred in the absence of exogenous androgens, it can be concluded that the expression of FGF-8 mRNA in these human cell lines, in the rat prostate and in other rat tissues is not under the regulation of androgens as hitherto proposed.