Melting and fragmentation of Ar and Ag clusters, containing from 30 to 500 atoms, have been studied with an isothermal molecular dynamics simulation method using classical forces. The simulations describe either evaporative decay or collisional dissociation. In the first case it has been found that the increase of the temperature leads to a continuous transition from a softening of the bonds to fragmentation and,with a proper scaling of the temperature, the effect is similar in Ar and Ag. During the collisional decay a perceptible fragmentation yield is observed in Ar whereas in Ag the input energy is converted into translational energy and rigid motions.