A cross-sectional study of the variation of blood-lead levels throughout pregnancy was carried out on 165 women living in a rural area and 19 women living in an urban area. The mean blood-lead levels of both groups did not differ significantly from those of non-pregnant controls (27 rural and 19 urban). There was, however, a significant decrease in blood-lead levels throughout pregnancy, the magnitude of which was greater than the dilution effect of the concurrent increase in plasma volume. Women living in the urban area, whether pregnant or not, had significantly higher blood-lead levels than did those in the rural area. The mean blood-lead levels of 23 neonates was significantly lower at 6 days than their mothers' at term. These observations suggest that throughout pregnancy there is either an increasing placental deposition of lead or an increasing rate of transfer of lead to foetal tissues or a possible increased loss of body lead via other routes, e.g., urine. The higher blood-lead levels observed for the urban populations reflect increased environmental contamination with lead.