D3H2LN mammary tumors grow rapidly and produce bilateral lymph node metastasis. Bioluminescent D3H2LN cells were injected into nude-beige mice, and tumor growth and metastasis were monitored over time in vivo. Data for a representative mouse are shown. Tumor take rate was high (6/8 mice) and lymph node metastasis to both the right and left thoracic areas was detected by week 9 in all mice with mammary tumors (upper panels). Ex vivo images of excised brachial lymph nodes and lung lobes are shown (middle panels). Histological analysis of the same tissues confirmed perfuse metastasis to the lymph nodes and isolated micrometastasis to the lung lobes (lower panels).