Basic fibroblast growth factor (FGF-2) is an important modulator of cell growth and differentiation under both physiological and pathological conditions. Until recently, most investigations into the FGF-2 signalling pathway were concerned with its interaction with specific membrane receptors. Nevertheless, while a 18 kDa protein of FGF-2 is cytosolic, there are also co-translated high molecular weight (HMW) isoforms that are predominantly located in the cell nucleus. An increasing amount of data strongly argue in favour of distinct biological functions depending on the subcellular location of the FGF-2 species. This review describes the evidence concerning the strictly intracellular mode of action of the HMW isoforms of FGF-2.