A series of 202 breast cancer biopsy specimens were analysed immunohistochemically for collagen IV to demonstrate basement membrane (BM) structures and blood vessels within tumour tissue. Integrity of the BM was graded into four categories and the number of vascular channels per square millimetre of tumour tissue were counted. Defective BM structures were significantly related to high grade, lack of tubule formation, invasive disease, high S-phase fraction and variability in nuclear size and shape. High vascular channel density was related to poor tumour differentiation and a high proliferation rate of cancer cells as well as to the absence of tubule formation, inconspicuous intraductal growth and low progesterone receptor content. High vascular density and defective BM structures were signs of poor prognosis and short recurrence-free survival in the entire cohort and also in local tumours. In multivariate analysis, the vascular density had independent prognostic value, as did the diameter, axillary lymph node status and mitotic rate. The counting of vascular channels within the tumour provides additional prognostic information in breast cancer, in contrast to analysis of the BM integrity which shows hardly any prognostic information additional to that provided by the special histological features, e.g. tubule formation and intraductal growth pattern.