Responses of Ca2+ oscillations to random perturbation are investigated at the conditions where the system stays at a steady state (before bifurcation point) or an oscillatory state (after bifurcation point). It is found that noise can induce both implicit and explicit internal signal stochastic resonance (IISSR and EISSR). In particular, the internal signal stochastic bi-resonance is also observed. When an external signal is added to the system, no IISSR or EISSR phenomenon occurs, implying an external signal destroys cooperation of Ca2+ signal and environment noise. (c) 2005 Elsevier B.V.. All rights reserved.