Four risk factors for overheating were sought in the histories of 34 cot-death victims in Oxford and Scarborough. 19 babies were unusually hot or sweating when found dead; 14 died in an unusually warm environment; 17 had evidence of a terminal infective illness; and 24 were excessively clothed or overwrapped. 3 babies had all four risk factors, 8 had three, 17 had two, and 4 had one risk factor. Only 2 had no risk factor; both had had very low birthweights. In 6 of 15 babies (40%) whose rectal temperature was recorded after death the temperature was above 37 degrees C, the highest being 42 degrees C. If parents could be educated to anticipate the dangerous situations preceding febrile apnoea, many cot deaths could probably be avoided.