The values of incoherent scattering functions are determined experimentally for 145 keV gamma rays in elements Au, Ag and Y at scattering angles 40°, 70° and 100°, using a x-ray gamma coincidence technique. The corresponding theoretical values are obtained from the tabulations of Hubbellet al, and computed from the models of Jauch and Rohrlich and Shimizuet al. A comparison between the theoretical and experimental results showed that the non-relativistic approach adopted in the theory of Shimizuet al is inapplicable to the present cases. A gross agreement is noticed between the present experimental results and the other theoretical values.