In setting up test procedures for radiation counter tubes, it is necessary to consider not only the test circuits but also the physical arrangements of test, such as nature of source, distance between source and counter, scattering by objects near the source or counter, shielding of the counter against unwanted radiations, and the background due to cosmic rays and general contamination. The relative importance of these various factors will depend on the type of counter under test. In selecting a room for counter-testing purposes, it is advisable to pick one as far as possible-from strong gamma-ray sources. It is particularly difficult to work in a room adjacent to one in which experiments are being performed involving the moving of a gamma-ray source from one location to another. A corner room is desirable from this standpoint. Attention should be paid to the fact that the intensity of cosmic radiation depends strongly on the altitude and on the amount of material above the counters. Also, in testing counter tubes that are physically long there may be a noticeable difference in the background counting rate, depending on whether they are tested in a horizontal or vertical position. When measuring background counting rates, it is preferable that the tube be in a lead shield to reduce the effects of local contamination.