Does a signal protein imbedded in a polyelectrolyte layer keep its activity? The study reported here demonstrates that cells can indeed interact with proteins incorporated in poly(L-lysine/glutamic acid) multilayer films. In contrast, poly(D-lysine) acts as a barrier to cell communication. For the case of monocytic cells the mechanism of contact with the active protein is elucidated. It is believed that such functionalized coatings could be useful tools for the modification of biomaterial surfaces with applications in, e.g., implants or tissue engineering.