A fall in haemoglobin noted in detainees in a Detention Centre in 1972 prompted a more detailed study to find possible reasons for this change. A significant fall in haemoglobin occurred between the first and third day after arrival, and no further fall had taken place eight weeks later. There was no evidence to suggest dehydration on arrival, or of any dietary deficiency during their stay. The fall in haemoglobin concentration occurred in non-smokers and smokers alike. It is suggested that the initial haemoglobin was higher than normal, possibly due to a physiological response to stress, and that it returned to normal by the third day when the boys had become accustomed to their new environment.