Sphingomyelin, phosphatidylserine, bovine lecithin and phosphatidylethanolamine modify the thermal stabilization of H2B-DNA complexes, by inducing stabilization at 0.3 and 0.6 H2B : DNA weight ratios and destabilify the arrangement of nucleohistone is confirmed by ultrastructural analysis which indicates a competitive action of these molecules during the nucleoprotein assembly. A possible regulatory role of phospholipids on native chromatin is proposed.