In order to identify regional lymph node drainage groups of primary malignant melanomas resp. suspicious pigmented tumors on truncal skin, lymphoscintigraphy using 99mTc-Sb2S3 colloid was performed in 50 patients of either sex prior to operative treatment. The lymphatic drainage pattern proved to be practically unpredictable by conventional anatomic guidelines based on the thesis of "lymphatic watersheds". In 96 per cent of the patients examined radiocolloid uptake was to be found in one or both of the axillary lymph node groups, either solely or combined with inguinal, supraclavicular, posterior cervical or parasternal node-bearing areas. In conclusion, axillary lymph node drainage groups are the center in lymphatic drainage from the truncal skin in man.