We report various nonlinear phenomena observed in the oxidation of ascorbic acid by molecular (H 2 Asc) oxygen in the presence of copper(II) ions in a continuous Ñow stirred tank reactor (CSTR) as well as in a batch reactor (closed system). Transient irregular oscillations were observed in a batch reactor by varying the initial concentrations of and copper(II) ions. The behavior of the system in a CSTR was studied by varying the H 2 Asc Ñow rate and the inÑow concentrations of and copper(II) ions. At low inÑow concentrations of (k f ) H 2 Asc copper(II) ions the system exhibits bistability and small amplitude regular oscillations. In a two-dimensional parametric plot with coordinates and the regions of bistability and oscillations form a cross-shapedFor increasing values of oscillations emerge H 2 Asc k f via a Hopf bifurcation and disappear due to a homoclinic orbit. Simultaneously applied small amplitude periodic and stochastic perturbations imposed onto the Ñow rate close to the bistable region revealed the phenomenon of stochastic resonance, which is conÐrmed by an analysis of probability distribution functions, power spectra, and singular value decomposition.