Of the several geophysical methods used in exploration for oil and useful ore bodies, the earth-resistivity and seismic-refraction tests have been found to be the most adaptable to the shallow tests generally required in highway construction work. Of these, the earth-resistivity test is the faster and has a wider range of application to highway problems than does the seismic test. Use of both methods of tests in subsurface explorations for engineering structures is expanding. The paper cites a growing need for a more thorough subsurface investigation of all engineering structure sites and gives examples of field data obtained by the Bureau of Public Roads when making preliminary geophysical surveys of proposed highway locations or structure sites. The economic aspects and the advantages and limitations of the two methods of test are discussed with particular reference to their application to highway engineering problems.