Infrared imaging has frequently been used in the past to detect changes in skin surface temperature associated with breast cancer. Usually a 1–2°C elevation in skin surface temperature is observed at the tumour periphery, and it has been proposed that this change is due to hypervascularity resulting from tumour-associated angiogenesis. In our study, we used the rat mammary adenocarcinoma 13762 MAT, a tumour that has been used to identify antiangiogenic drugs, to investigate whether infrared imaging can detect angiogenesis in malignant tumours. If successful, it was hoped that this technique would represent a simple, noninvasive, procedure for monitoring the activity of antiangiogenic drugs. It was found that, unlike breast cancer patients, no tumour-associated increase in skin surface temperature was observed, but a constant and highly significant reduction in temperature was noted that was independent of tumour size and was produced by relatively small tumours (≥ 0.5 cm in diameter). The explanation for this effect is unclear but it may be due to the poorly vascularised nature of rapidly growing tumours. Nevertheless, our study indicates that the peripheral temperature elevation reported in breast cancer patients is unlikely to be due to hypervascularity resulting from tumour-induced angiogenesis. An alternative explanation is that the temperature increase is due to a chronic inflammatory response around developing breast tumours. With increasing evidence that inflammation can enhance tumour growth and is associated with a poor prognosis, this suggestion implies that infrared imaging may have considerable prognostic value. © 2003 Wiley-Liss, Inc.