Ferritin levels in serum and milk were investigated in series of 15 urban and 18 rural black mothers. No mother was anaemic. Mean serum ferritin levels in the urban and rural groups were 57 +/- 55 ug/l and 25 +/- 28 ug/l (mean +/- SD). Corresponding milk ferritin concentrations were 21 +/- 22 ug/l and 29 +/- 30 ug/l respectively. The significance of ferritin in human milk is discussed.