The phase transition at Tc=0, caused by variation of parameters in a lattice dynamic system, is studied by means of classical and quantum-statistical mechanics. We calculate the critical exponents explicitly. They differ from those for Tc 0. Within the frame of classical statistical mechanics they are nonuniversal, depending on a parameter. This feature is suppressed, however, by quantum fluctuations. The quantum-mechanical Tc=0 critical point for a d-dimensional system corresponds to the Wilson fix point of a (d+1)-dimensional system. © 1977 The American Physical Society.