Meteorological observations from the Viking landers showed that baroclinic waves on Mars are much more periodic than those seen on Earth. A global circulation model of the Martian atmosphere, with simplified parametrizations of heating and friction, has been used to examine baroclinic waves in the parameter range appropriate to the Martian atmosphere. Two distinct flow regimes are found to be dependent on the magnitude of thermal and frictional dissipation. The flow is composed of small-amplitude disturbances propagating around a zonally oriented midlatitude jet in an irregular fashion or a highly persistent large-amplitude zonal wavenumber 3 wave. The large-amplitude waves are much like those seen in differentially heated rotating annuli. It is shown that the large amplitude waves are not the linearly most unstable modes of the system, rather nonlinear effects are dominant. Attractor reconstructions, using empirical orthogonal functions, show the regime transition as a bifurcation from a messy aperiodic attractor to, what is essentially, a limit cycle. Analysis of the potential vorticity budgets of the large-amplitude waves shows that a large free mode component is present. A mechanism is suggested whereby the sources and sinks of potential vorticity balance departures from the free mode form, thus maintaining the large-amplitude waves. ¿ American Geophysical Union 1995