Investigations of radio propagation at 35 and 150 mc into large city buildings have disclosed that, on the average, a loss in the order of 20 to 25 db may be encountered on the first floor. This loss, which represents the reduction from the median field in the city streets at the same distance from the transmitter, is known as building loss. Losses were found to be slightly smaller and more uniform at 150 mc than at 35 mc. Losses also were found to be appreciably less on higher floors in a building. Methods of using this information for engineering radio systems to serve people in buildings are described. Some sample problems demonstrate that, with equal receiver performance,the effective coverage range in buildings for a 150-mc system will be greater than that for a 35-mc system.