The effects of sodium n-dodecyl sulphate (SDS) on the structure of histone HI has been studied by a combination of e:quilibrium dialysis, U.V. spectroscopy ; polyacrylamide gel electrophoresis, protein titration and viscometery techniques using, 2.5 mM phosphate buffer, pH 6.4. The interaction of H, and SDS in contrast tomanyothel-protein-SDS interactions is organized between V 40 to 70. Above V=40 there is an exothermic contribution from HI folding characterized by minima in the enthalpy curve at about 65 Kj mol:' This subject has been confirmed by spectroscopy, electrophoresis , titrametery and viscometery techniques