In situ as well as extra situm cytochemical methods were used to investigate why the observed Feulgen-DNA value of sperm versus lymphocyte cells is lower than expected. After treatment with 5 N HCl, in situ experiments involving the GCA reaction and the UV cytophotometry showed the loss of DNA in sperm nuclei to be 12% more than that in lymphocyte nuclei. Extra situm study of sperm and lymphocytes treated with 5 N HCl showed the phosphate and DABA contents of sperm to be 35% and 23%, respectively, less than those of lymphocytes. The data suggest that sperm chromatin is much more sensitive than somatic chromatin to HCl depolymerization during the Feulgen reaction, and this can tentatively be attributed to the protein complement of sperm chromatin.