Previous studies on aqueous solutions of HCO-(Val-Pro-Gly-Gly)40-Val-OMe indicated an increase in secondary structure on increasing the temperature implying a concomitant intramolecular hydrophobic association. Nuclear Overhauser enhancement (NOE) studies are reported which explicitly demonstrate an increase in association of γCH3 of Val and δCH2 of Pro protons on increasing temperature. The analogue where Ala replaces Val does not show this inverse temperature transition. These results provide direct demonstration of the "hydrophobic effect" responsible for inverse temperature transitions in aqueous systems. © 1977.