Clinical and pathological evidence of overheating was sought in a consecutive series of infants dying in Newcastle and Gateshead. In 8 of 33 cases of cot death investigated pathologically histological changes in the small intestine of the kind described in association with heatstroke were seen. Such changes were not seen in any of 12 deaths from chronic or congenital conditions, and in only 1 of 8 acute explained deaths--in a baby who died with necrotising enterocolitis. 15 of 34 cot-death babies investigated clinically were judged to have been excessively clothed or covered at the time of death. 7 babies were unusually hot when found dead, and 4 others had been noticed to be hot shortly before death. 10 more babies had evidence of a terminal infection without observed fever. The possibility that overheating contributes to some cot deaths has important implications for health education.