The sex chromosomal constitution has been determined in various types of human leukocytes at interphase by use of fluorescence in situ hybridization with X- and/or Y-specific DNA probes. It is found that during aging and differentiation of myelocytes into polymorphs there is no significant change in the relative frequency of various types of male and female cells with a specific type of sex chromosomal constitution. Non-random variability of the relative proximity between the X chromosomes within the nuclei is also observed in female cells. Moreover, we are the first to determine that sex-specific "drumsticks" and "sessile nodules" in female polymorphs originate from the X chromosomes and that non-sex-specific "drumstick-like" bodies in male polymorphs are of Y chromosomal origin.