It is proposed that the core of the Earth where metal hydrides are subject to high pressure and temperature conditions is a suitable site for ‘‘cold‐nuclear’’ fusion to proceed. This is compatible with recent experimental evidence, that shows that low levels of cold‐nuclear fusion may take place in hydrides, that hydrogen is soluble in iron at high pressures, and in some models up to 0.4% by weight of the core of the Earth may be hydrogen. If it is assumed that3He is produced within the Earth by cold‐nuclear fusion, and production and escape to the atmosphere has attained steady‐state, the terrestrial fusion rate &lgr;fis between 0.3×10−25to 4.4×10−25fusions per second, per deuteron. In contrast to terrestrial radiogenic heat production, cold‐nuclear fusion can produce only 10−5of the observed terrestrial heat flow.