Splenocytes and column-separated T cells are differentiated into subpopulations of T and B cells on the basis of computer-assisted morphometric analysis of Feulgen-positive nuclear DNA. Differentiation is based upon the analysis of computable image information related to DNA distribution patterns. The technique at the present time does not allow immunofluorescent and morphometric measurements to be made on a given cell. However, the differentiation obtained by using descriptors proven capable of detecting pure populations of T and B cells shows excellent agreement with the differentiation obtained by immunofluorescence analysis. The descriptors and decision rules used the discrimination among splenocytes are reproducible from one experiment to another and remain valid for the differentiation of lymphocytes from animals of different sex and strain.