The plasma membrane represents an impermeable barrier to proteins and other macromolecules. However, certain exogenous proteins are able to cross cellular membranes and gain access to the cytosol. The best examples are bacterial and plant protein toxins, acting on intracellular targets. During last few years the number of known proteins possessing the capability to cross cellular membranes in the reverse direction and reach the nucleus has increased (acidic and basic fibroblast growth factor, interleukin 1, angiogenin, Schwannoma derived growth factor, homeoprotein Antennapedia, HIV-1 Tat protein are some examples). Here, the role of transport of exogenous acidic fibroblast growth factor to the nuclear location as a part of the growth factor signaling is discussed, and the current knowledge on this issue is reviewed.