The effect of heat at low pH (3.6) on the conformation of arachin, the major reserve protein of the peanut has been investigated by intrinsic viscosity measurements, UV difference spectroscopy, fluorescence spectroscopy, spectrophotometric titration of tyrosine and near and far UV circular dichroism (CD). Results are presented in figures and fully discussed. Heating of arachin at 90 degree C at pH 3.6 for 15 min caused an increase in the intrinsic viscosity. UV difference spectra showed a blue shift consisting of 2 troughs (at 278 and 287 nm) which deepened as the temp. or length of heating time increased. The unavailability of 8 tyrosine groups for titration after heating at 90 degree C for 15 min at pH 3.6 suggested that the protein was not completely denatured by such treatment. Near CD spectra showed a weakening of all CD bands as the pH was lowered from 7.5 to 3.6 and as heating progressed, indicating a loss of tertiary structure. Far CD spectra showed a shift of the spectral minimum from 210 to 205 nm following heating at 90 degree C for 15 min at pH 3.6. The role of denaturation in the heat-induced gelation of arachin at pH 3.6 is discussed.