A master equation approach is used to study the influence of internal fluctuations on the dynamics of three excitable thermochemical systems exhibiting continuous as well as discrete changes of temperature. The systems differ by the types of excitability. The dependences of the relative deviations from mean values of the interspike intervals and escape times from the stable stationary state on the size of the systems calculated from simulations of stochastic trajectories exhibit minima, which testify to the appearance of resonance phenomena. An explanation for the appearance of the stochastic resonances is presented.