Arm volumes of 360 patients with breast cancer were determined by a new optoelectronic technique. About 42% developed swelling of the arm after modified radical mastectomy which varied from mild (edema-volume 150-400 ml), moderate (400-800 ml), to severe (more than 800 ml) lymphatic edema. Lymphscintigraphy and computer tomography of the arms was also studied in different grades of lymphatic edema. Two years after operation and telecobalt-irradiation, one half of the patients without arm edema showed marked signs of a decreased capacity of lymphatic transport. In patients with severe lymphatic edema, the dynamic as well as the static evaluation of the lymphscintigrams revealed delayed transport, lack of radioisotope accumulation in the axillary region and notable congestion in the upper arm and forearm. Computerized tomography displayed a shift of fluid volume in the epifascial and subfascial tissue compartments and detected progressive structural changes in the soft tissue. Moderate edema not only increased the epifascial but also the subfascial compartments. In severe postmastectomy arm lymphedema, however, expansion of the epifascial space was paradoxically sometimes associated with a decrease in the subfascial compartment.