We looked at risk of early pregnancy loss among 171 women who conceived while participating in study. Twenty-five percent of biochemically detected pregnancies ended within six weeks of the last menstrual period; all but two of these losses were clinically unrecognized. While our sample is small, it is the first to allow description of possible associations between risk of early pregnancy loss and maternal characteristics or exposures. We looked at risk in relation to a woman's age, pregnancy history, weight, education, prenatal DES exposure, cigarette smoking, use of caffeinated and alcoholic beverages, marijuana, cigarette smoking by baby's father, and other variables. None of these factors was definitely associated with early pregnancy loss. Still, the possibility of real effects cannot be excluded and deserves further study.