Detection of Hg, Cd, and Pb within concrete matrices located in 8-gal drums was successfully demonstrated using a pulsed gamma neutron activation analysis system. Real-time assays of 600 s led to the detection of these metals at concentration levels ranging, in parts per million (ppm) by weight, from 487 to 19 820 for Hg, 485 to 8181 for Cd, and 9927 to 19 950 for Pb. The measurements of Hg and Cd relied on the observation of thermal neutron-induced prompt gamma rays, whereas the Pb measurements relied on the observation of decay gamma rays from 207mPb, a product of fast neutron-induced reactions in Pb. The projected lower limits of detection of the current system for a 600-s run are 15, 170, and 8600 ppm for Cd, Hg, and Pb, respectively. Up to a one-order magnitude of improvement in sensitivity is anticipated through the enhancement of the system's detector and neutron source. The results obtained confirm the potential of prompt and decay gamma neutron activation analysis as an effective method for the nondestructive analysis of hazardous metals in mixed-waste drums.