The linearized dispersion relation describing waves in a plasma having a uniform magnetic field, uniform density, and inhomogeneous parallel (to the magnetic field) flow is generalized to include thermal anisotropy (Ti⊥/Ti∥), a key feature existing in many space and laboratory plasmas. The growth rate and the real frequency at which the maximum growth rate occurs for the ion acoustic mode increases with increasing Ti⊥/Ti∥. The propagation angle, with respect to the background magnetic field, for ion acoustic waves is shown to depend on Ti⊥/Ti∥. Also presented is a generalized calculation of experimentally relevant perturbed distribution functions to include shear in the field-aligned flow.