Abstract: A flow cytometry apparatus for determining one or more characteristics of particles or the like flowing in a liquid stream includes a nozzle for generating a liquid flow stream for moving particles therethrough substantially one at a time. A light source provides a beam of light to illuminate the particles moving in the stream. An optical path for light scattered and fluorescence emitted by each moving particle has an axis which preferably makes a 90.degree. angle with respect to the axis of the illuminating beam. A beam splitter is positioned in this optical path with an angle of incidence greater that 45.degree. so as to transmit fluorescence and to reflect light scatter. Detectors are provided for detecting the transmitted fluorescence and the reflected light scatter and for associating the scattered light and fluorescence with one or more characteristics of each particle.