The properties‐of certain plastic substances have been examined with the idea of using them to construct solid lenses for focussing ultrasonic radiation. Some experiments are described which illustrate the advantages offered by such lenses. The use of a plano‐cylindrical or a plano‐spherical lens permits a reduction to 1/10 or 1/100 respectively of the energy which must be emitted by a quartz crystal to produce a given intensity of ultrasonic radiation over a given region.