In ultrasonic attenuation experiments carried on by the pulse method, it is important to know the part of the measured attenuation contributed by diffraction in the ultrasonic field. In certain cases, particularly at the lower megacycle frequencies, the diffraction loss can be much greater then the attenuation intrinsic to the specimen. The diffraction loss in decibels has been computed elsewhere as a function of the distance the ultrasonic pulse travels back and forth in the sample. Here an expression for the increment to the attenuation is derived taking into consideration which echoes the decibel drop is measured. It is shown that the first echo has suffered a considerable loss at the lower frequencies and that one must consider that loss in computing the increment to the attenuation caused by diffraction if he has used that echo as one at which the decibel loss is measured. If that loss is not considered, the incremental attenuation will be excessive.