Within the two state theory (TST) for stochastic resonance (SR) we analize two different aspects: (a) the extension of the TST in order to include potential asymmetry (i.e.: the states show different stabilities); (b) the evaluation of transition rates for systems whose stationary distribution is non Gaussian. We apply the results of (a) to study the role of the potential symmetry for SR in bistable systems, observing that the signal-to-noise ratio increases with the symmetry of the potential of the system indicating that it is this feature that governs the optimization of the response. We apply the results of (b) to discuss SR in situations where we can assume that the noise is non Gaussian, and discuss its relation with experimental results in sensory systems.