Burkitt's lymphoma was diagnosed in a patient during the third trimester of pregnancy. Treatment was high-dose, intermittent cyclo-phosphamide initially gave a good response which permitted the pregnancy to be carried to term. The infant was normal at birth and had a normal white blood cell count and hematocrit, despite leukopenia in the mother, and he still remains normal at the age of 12 months. Results in this patient and a survey of reported cases in which cyclophosphamide was administered during pregnancy lead to the conclusions that low-dose oral therapy is the least hazardous regimen early in pregnancy while late in pregnancy, large doses administered intravenously may be tolerated without fetal damage.