In order to examine tumour growth in sympathetically denervated murine skin, two breast cancer tumour lines were employed, i.e. M3 tumours, of a relatively high local growth and low metastatic capacity, and MM3-LN tumours, that grew locally at a slower rate but disseminated early to the lung. Mice subjected to unilateral superior cervical ganglionectomy or sham-operation 2 weeks earlier were used. M3 or MM3-LN tumours were implanted in the ipsilateral ear to the surgical procedure. Tumour size was assessed every 2-6 days, starting from the 7th day after tumour implantation. Growth of M3 and MM3-LN tumours was significantly slowed by a previous sympathetic denervation of the skin territory. There were no significant differences in the number or size of pulmonary metastases at autopsy between mice subjected to ganglionectomy or to sham-operation. Ganglionectomy increased significantly ipsilateral submaxillary lymph node ornithine decarboxylase activity by 62% and decreased noradrenaline content to 8% of the innervated contralateral lymph node. The present results indicate a local inhibitory modulation of tumour growth by the sympathetic nervous system.