  The dynamics of two 12-monomer heteropolymers on the square lattice is
studied exactly within the master equation approach. The time evolution of the
occupancy of the native state is determined. At low temperatures, the median
folding time follows the Arrhenius law and is governed by the longest
relaxation time. For good folders, significant kinetic traps appear in the
folding funnel whereas for bad folders, the traps also occur in non-native
energy valleys.
