The cell is a complex system functioning outside a thermodynamic equilibrium. The prediction of cellular functions based exclusively on molecular evidence is still impossible because of the large number of interacting molecules and the nonlinear interactions between cellular subsystems. The system cell displays a surprisingly small spectrum of macroscopically observable degrees of freedom. Their number and characteristics, however, are different in normal and neoplastic growth. As illustrated by image analytical, microanalytical and other cell biological data we demonstrate that certain cellular observables--termed order parameters--may serve as indicators for normal and neoplastic growth. The data indicate that the transition between normal and neoplastic growth can be understood as a phase transition of the mitogenic signalling network. In this interpretation, the order parameters of normal and neoplastic cells are the result of cellular self-organization.