The diagnosis of soft tissue disease such as cancer by radiographic means depends to some extent on the difference in the attenuation of gamma -rays in healthy and diseased tissues. Since devices for imaging very small changes in attenuation are now being introduced, a more exact knowledge of such attenuation coefficients in various tissues would be of help in the prospective evaluation of such techniques. Using gamma -rays of different energies, the authors have measured the attenuation coefficients of normal and cancerous tissues taken at autopsy with an accuracy of 0.5% at the 95% confidence level. The results of such measurements were presented and discussed.