Aim: To simultaneously determine the localization of histones and protamines within human sperm nuclei. Methods: Immunofluorescence of the core histones and protamines and fluorescence in situ hybridization of the telomere region of chromosome 16 was assessed in decondensed human sperm nuclei. Results: Immunofluorescent localiza- tion of histones, protamine 1 (PRM1) and protamine 2 (PRM2) along with fluorescence in situ hybridization localiza- tion of chromosome 16 telomeric sequences revealed a discrete distribution in sperm nuclei. Histones localized to the posterior ring region (i.e. the sperm nuclear annulus), whereas PRM1 and PRM2 appeared to be dispersed throughout the entire nucleus. Conclusion: The co-localization of the human core sperm histones with the telomeric regions of chromosome 16 is consistent with the reorganization of specific non-protamine regions into a less compacted state. (Asian J Androl, 2008 Jul; 10: 535-541)