Haematological indices were studied serially in 33 healthy women, at one week before delivery, during the first six days of the puerperium, at six weeks and six months post partum. Red cell count, haemoglobin concentration and haematocrit decreased during the first four days of the puerperium; haemoglobin concentrations up to 3.5 g/dl less than pre-delivery values were recorded in the absence of clinical postpartum haemorrhage. The second puerperal day haemoglobin concentration correlates most closely with the six week postpartum value. A leucocytosis of greater than 20 X 10(9)/1 was found on the first puerperal day in 15 per cent of the women studied.