In the search for deposits of radio-active minerals the Bureau has used scintillometer equipment mounted in a D.C.3 aircraft with considerable success in suitable country. In order to investigate the possibility of extending the application of this type of survey to mountainous country, over which the D.C.3 could not be used, tests of similar equipment mounted in a helicopter have been made over three areas in New South Wales. The areas selected were at Carcoar, Tenterfield and Broken Hill. The results of the tests indicate that a scintillometer mounted in a helicopter can be successfully used in almost any type of country. However, in areas of low relief, the D.C.3 aircraft is preferable, owing to its greater speed and to the fact that it can carry auxiliary equipment by means of which its position at any time can be accurately fixed. The helicopter will not give the rapid and complete routine coverage of large areas that is given by the D.C.3. In rugged or mountainous country where the larger aircraft cannot be used the helicopter offers great advantages over other methods of prospecting for radio-active deposits. For this work it is best operated by following flight lines related to easily identifiable map features.