An important part of man's radioactive environment is the natural radioactivity of soils. This radioactivity varies with soil type and with depth in the soil profile. The relation between gross gamma activity and soil depth for a particular soil (Miami silt loam) is presented, together with a discussion of the contribution of K 40 and the uranium and thorium series and of the effects of fallout from bomb tests in increasing the radioactivity of a thin layer of surface soil.