A flow cytometry nozzle and method for orienting sperm cells in a fluid flow path including an interior surface of a nozzle. The interior surface of the nozzle having a first, a second and a third axially tapered region for progressively accelerating the speed of a fluid stream in a downstream direction toward a nozzle exit. At least two of the regions having generally elliptical cross sectional shapes oriented in different directions for applying torsional forces to a fluid stream passing there through, tending to bring sperm cells in the stream into a desired orientation.