Underground cavities having dimensions of tens to hundreds of meters should markedly reflect artificial seismic waves and locally obstruct reflections from deeper horizons. Attempts have been made to apply these principles to delineate solution-mined cavities in bedded salt. In one area results from a brine-filled cavity 300 m below the surface were unclear, but in a seismically favorable area strong 'shadows' were found in a reflection survey of cavities 500 m below the surface. At present the method requires good reflecting horizons both above and below the layer to be explored. Among other applications, the method should be useful in mapping natural caverns and nuclear-blast cavities.