To examine the hypothesis that lymphatic dissemination in breast cancer occurs sequentially. Thirty patients with clinically localized adenocarcinoma were studied. Patent blue dye was administered into the tumour at the beginning of a modified radical mastectomy or segmental mastectomy with en bloc axillary lymph-node dissection (ALND). In the removed specimen, blue-stained lymphatic channels were dissected from the primary tumour to the first draining lymph node(s) (sentinel node(s)). Identification of a sentinel node (SN) was successful in 26 patients (87%). In 10 patients the SN was tumour-positive. In six of these patients, the SN was the only tumour-positive node. There was no incidence of 'skip' metastasis. This study confirms the sequential nature of lymphatic dissemination. When confirmed in vivo, these data may lead to a substantial reduction of the need for ALND without compromising survival and regional control and without loss of prognostic and staging information.