AbstractThe effect of mitogens on the degree of polarization of the fluorescence from viable human lymphocytes, labeled with fluorescein, have been reported to be different in cells from subjects with malignant disease as compared with those from healthy donors. This has potential applications in the field of clinical diagnosis and a flow cytometer could be the instrument of choice for this purpose. We believe that such an instrument should be simple and easy to use and a flow cytometer was assembled with this in mind and with the object of gaining experience which would provide the basis for a future finalized design. The instrument is suitable for use in other biologic applications where polarization is of interest and also as a general purpose flow cytometer. Its main features, its characteristics and a preliminary performance report are presented here.