The effect of long term ascorbic acid (AA) supplementation (3g per day) on 27 women with early breast cancer has been investigated. For comparison a similar but limited study was carried out in patients with benign breast disease. The responses of leucocyte levels of AA to supplementation provided some evidence to suggest that the metabolism and utilisation of the vitamin may be different in these patients. In addition longitudinal measurements of urinary hydroxyproline/creatinine (OHPro/Cr) ratio were carried out in these patients. The long term ingestion of AA did not appear to affect the prognosis of the disease in the early breast cancer group. Similar 5 year survival rates were seen in the unsupplemented and supplemented cancer groups.