Previous studies at the Bureau of Mines outlined the hazards of ammonium nitrate-fuel oil (AN-FO) mixtures in the presence of pyrite- bearing ores. The recent trend in the mining industry to strengthen AN-FO by the addition of aluminum metal raised the question regarding the effect of aluminum in AN-FO in the presence of pyrite- bearing ore. Laboratory work, similar to that done previously, demonstrated that the temperature of a self-sustaining reaction in the presence of AN-FO ore-aluminum is not lower than that for a comparable AN-FO-ore mixture. However, as might be expected from known thermochemical data, once initiated, the resulting reactions between AN-FO, aluminum, and pyrite are much more vigorous than those observed for AN-FO and pyrites alone. The temperature required to produce a self-sustained reaction for the combinations tested in this study is 250 deg +- 20 deg f while in the previous Bureau study, reactions were noted, in some instances, at 150 deg f. The different pyritic ores may be the cause of this variation.