The predictive value for cancer recurrence of five measurements of haemostatic activity was studied in 89 patients with operable breast cancer. Neither preoperative nor sequential measurements up to 9 months postoperatively of fibrinopeptide A, fibrin fragment B beta 15-42, fibrinogen and serum fibrin(ogen) degradation products nor the fibrin plate lysis assay correlated with early recurrent disease. B beta 15-42 values were higher preoperatively in patients with oestrogen receptor positive tumours (P = 0.017). Mean B beta 15-42 values rose postoperatively (P = 0.003), largely because of an increase in patients with oestrogen receptor negative tumours.