Tissue Polypeptide Specific-Antigen (TPS), a marker of cell proliferation, was evaluated in 258 patients, 216 with breast carcinoma and 42 with benign breast disease. TPS was measured pre-operatively in 98 patients and correlated with stage of disease showing a progression from Stage I through to Stage IV disease. TPS increased with increasing tumour size, however, TPS levels did not correlate with the number of involved lymph nodes. TPS was measured during follow-up in 118 patients, 64 had no evidence of recurrence, 23 had evidence of loco-regional recurrence and 31 had evidence of metastatic disease. TPS levels were significantly elevated in all categories of recurrence and were highest in patients with disseminated disease. Patients with elevated TPS during follow-up were more likely to experience disease progression on further follow-up. This preliminary study demonstrates that this marker may be useful as an index of tumour burden and deserves further evaluation in a large population to determine whether it can aid in the identification and follow-up of patients with recurrent disease.