A rheological study of a series of thermotropic liquid crystalline copolyesters containing varying proportions of hydroxybenzoic acid, isophthalic acid, and hydroquinone has shown unexpected behavior. Certain compositions were observed to exhibit a POSITIVE temperature coefficient of viscosity (viscosity increasing with shear rate) over the entire shear rate range. Other compositions showed flow curves which intersected at critical shear rates. This behavior is explained by a variation in chain stiffness with composition (high hydroxybenzoic acid content resulting in stiffer chains) which results in a biphasic melt. The unusual rheological behavior is a manifestation of the competition between isotropic and anisotropic phases, which is influenced by composition, temperature, and shear.