We have investigated the relationship between immunohistochemically determined p53 status and outcome in 277 women with node-positive primary breast cancer who, following tumour excision and axillary clearance, were randomised to receive either 6 cycles of cyclophosphamide/methotrexate/S-fluorouracil (CMF) (n = 130) or no such post-operative treatment (n = 147). Follow-up data (median = 9 years) were available on all patients. A significant association was found between p53 status and survival. Patients with p53-positive tumours had a less favourable outcome than those with p53-negative disease. Women receiving adjuvant CMF chemotherapy had a significantly more favourable outcome compared to those who did not. The effect was seen both in women with p53-positive and p53-negative tumours; multivariate analysis showed relative risks for overall survival attributable to chemotherapy of 2.3 (95% CI 1.2-4.3) for women with p53-positive tumours and of 2.1 (95% CI 1.4-3.0) for those with p53-negative tumours. Thus, adjuvant chemotherapy with CMF is associated with a survival benefit in women with node-positive breast cancer irrespective of immunohistochemically determined p53 status.