Synthetic line profiles are generated for a variety of model atmospheres containing linear and quadratic velocity fields. Both weak and strong lines are considered. Comparison of the actual velocity structures with those inferred from the bisector shifts of the asymmetrical profiles show qualitative agreement only in the line cores and in general only for velocities small compared with the thermal velocity. Approximate expressions relating the observed profile parameters to atmospheric velocity parameters, for small linear velocities, are obtained and tested. Observed rms displacements in the solar Ha line are used to infer the amplitude of the oscillatory velocity field in that region of the solar chromosphere where the core is formed.