An infrared camera was used to study the formation and dynamics of hot zones normal to the flow direction on the surface of a radial-flow reactor placed horizontally, inside a vessel. The test reaction - the atmospheric oxidation of carbon monoxide-exhibited steady-state multiplicity. Slow cooling of the vessel caused a shift from a fully-ignited state to one with a hot Zone in the center of the reactor bounded by, cold zones at both reactor ends. The hot zone was separated by sharp temperature fronts from the adjacent cold zones. It shrank upon further cooling of the vessel and eventually extinguished. In certain cases, two stable states existed for the same operating conditions with qualitatively different hot zones and reaction rates. A slow back-and-forth motion of the temperature fronts (breathing) caused complex oscillations in the overall reaction rate. The dynamic features of the two fronts were different in sonic cases due to nonuniform catalytic activity, and inefficient thermal dispersion. The amplitude and frequency of the temperature breathing motion increased upon cooling of the vessel containing the reactor. Experiments suggest that transversal hot zones are likely to form in packed-bed reactors close to the extinction temperature.