Seven West African infants were studied prospectively from birth to 1 year to investigate factors affecting sleeping metabolic rate (SMR), particularly acute infection. There was no rise in SMR associated with acute infection, after adjustment for the effects of changes in body weight and body temperature. In the case of two illnesses, malaria and 'fever', there were falls in adjusted SMR. It is suggested that these falls can be accounted for by the effects of altered energy intake. Other effects on SMR were in close agreement with previous work.