In this blind prospective study of breast scintiscanning with 99Tcm-diethylene triamine penta-acetic acid (DTPA) in 67 female patients presenting at a primary breast referral clinic, we have observed that this investigation has a high diagnostic accuracy in distinguishing benign from malignant lesions of the breast. The predictive value of the test when positive in establishing the presence of cancer is 94 per cent with a false negative rate of 6 per cent. The predictive value of the test when negative in excluding cancer in 97 per cent with a false positive rate of 3 per cent. Initial studies also indicate the potential value of DTPA breast scintiscanning in delineating the activity of painful benign lesions of the breast.