Numerical simulations of the effects of buoyancy on the stability and morphology of Taylor-Couette flow have been conducted. The three-dimensional equations of motion are discretized using a hybrid Chebyshev collocation/Fourier spectral method. The problem geometry consists of an air-filled vertical annulus with radius ratio, ϭr i /r o ϭ0.5 ͑where r i and r o are the inner and outer radii, respectively͒, and aspect ratio, ΓϭL/(r o Ϫr i )ϭ10 ͑where L is the height of the annulus͒. The flow is generated by combined heating and rotation of the inner cylinder. Results for various values of the Reynolds number, Re, and Grashof number, Gr, show several bifurcations of the system. The most notable change in flow structure with increasing rotational effects is the onset of spiral flow in certain parameter ranges. Compared to existing analytical and experimental results, the current numerical results show good agreement.