A quantitation scheme for absolute activity measurements with the gamma camera is presented. The technique relies on the use of a set of derived buildup factors to correct for the effects of scatter. Only anterior and posterior view count rates of the region of interest are required for quantitation. The buildup factors are reported for various depths for two different source sizes using the parallel-hole collimator with a specific window setting. Phantom studies have shown that the method provides less than 5% error for activity determinations at all investigated depths.