AKR/J mice (carrying the AK-virus leading to a high spontaneous incidence of thymic lymphoblastic lymphoma) exposed to 50 Hz ELF at 1 or 100 tesla for 24 hr/day, 7 days/wk over their lifetime. Animals were checked daily and weighed and palpated weekly. Starting at 6 months, blood samples were taken monthly from the tail. There was no effect of magnetic field exposure on body weight gain or survival rate, and lymphoma incidence did not differ between exposed and sham-exposed animals. Therefore, these data do not support the hypothesis that chronic exposure to 50 Hz magnetic fields is a significant risk factor for developing leukemia. The authors provide rationale for the study as investigating whether high residential exposure to 50 or 60 Hz magnetic fields might increase the risk of leukemia, especially in children.