The effects of quenched site and bond dilution in the three-dimensional three-state Potts model are studied via the microcanonical simulation. In both systems we observe the following picture as quenched dilutions are added: the line of first order phase transitions originating with the pure system terminates at a tricritical point, and the resulting second order phase transition line has a continuously decreasing specific heat exponent for increasing dilutions. © 1989.