Secondary lymphedema is a localized, acquired lymphatic microcirculatory disturbance that affects large numbers of patients after breast cancer therapy. There is a paucity of objective methods to quantitate lymphatic function and to anticipate the response to therapeutic interventions. We applied radionuclide lymphoscintigraphy to evaluate lymphatic transport and axillary lymph node visualization in women following breast cancer therapy to determine the utility of these data in these patients. Lymphoscintigraphy was performed after subcutaneous injection of 0.25 mCi of Tc-filtered sulfur colloid. Subcutaneous accumulation of radiotracer ('dermal backflow') and the visualization of axillary lymph nodes were graded using our own scoring system. The ratio of radioactivity within the affected to normal axillae (ARR) was also quantified. Nineteen patients with lymphedema after breast cancer therapy were evaluated. The disease severity was documented by serial measurements of the limb volume using the truncated cone formula. Responses to therapy were quantified after completion of the therapy. There was a correlation between the ARR and the percentage reduction in edema volume. The lymphoscintigraphic score correlated with the initial arm volume excess and with the durationof lymphedema. It can be concluded that quantitative and semi-quantitative assessment by radionuclide lymphoscintigraphy represents a potentially useful tool for the clinical assessment of upper extremity lymphedema.