Although evidence tends to suggest that high levels of lead exposure increase the risk of spontaneous abortion, we do not yet know whether moderate- to low-level exposure elevates risk. Among 351 women (aged 16 to 35 years, with single pregnancies) who were registered for a longitudinal study, 15 (4.3%) women experienced spontaneous abortion after the 12th week of gestation and before the 20th week. We collected participants' blood samples during the first trimester of pregnancy (8-12 weeks) for lead measurement by inductively coupled plasma-mass spectrometry. Mean +/- standard deviation of blood lead was 3.8 +/- 2.0 g/dl (range 1.0-20.5 g/dl) with a geometric mean of 3.5 g/dl. Mean blood lead concentrations did not differ significantly between spontaneous abortion cases and ongoing pregnancies (3.51 +/- 1.42 and 3.83 +/- 1.99 g/dl, respectively). The findings suggest that in apparently healthy women, low blood lead levels (mean 5 g/dl) measured in early pregnancy may not be a risk factor for spontaneous abortion.