The record of 18 patients with Stage II Hodgkin's disease and large mediastinal masses, who received radiation therapy as sole treatment for their disease, were reviewed. The ratio of each patient's maximum tumor diameter to his maximum transthoracic diameter was measured from radiographs taken prior to treatment, and at two intervals approximating 1/3 and 2/3 the total radiation dose. The slopes of the resulting graphed data points were correlated with patient outcomes. No correlation could be drawn between prompt or slow tumor regression and freedom from tumor recurrence. It is concluded that the rate of tumor mass regression in Hodgkin's disease is not predictive of the ultimate success or failure of radiation therapy, and should not be used as a criterion by which to judge the need for additional systemic chemotherapy.