The densities of the elements have been found to be a periodic function of the atomic number in the same manner as the other properties of elements in the Periodic Table. The existence of pressure‐induced polymorphic transformations in solid elements at room temperature is found to be closely correlated to the periodicity of density, hence, the atomic number. With only the exception of Fe, no phase transformations have been found for 28 solid elements having densities greater than &rgr;=2.8+0.12Z. For elements having densities less than the above value, there might be only two exceptions out of 50 solid elements that do undergo pressure‐induced phase transformations within the range of presently available apparatus. This correlation seems to serve as a better indication for finding a high‐pressure phase than is predicted on the basis of crystal structure, and has led the author to find a high‐pressure phase in Se, Tm, and Lu.