Abstract: A method for determining if tissue is malignant as opposed to non-malignant (i.e., benign tumor tissue, benign tissue, or normal tissue), In one embodiment, the method comprises irradiating a human breast tissue sample with light at a wavelength of about 310 nm and measuring the time-resolved fluorescence emitted therefrom at about 340 nm. The time-resolved fluorescence profile is then compared to similar profiles obtained from known malignant and non-malignant human breast tissues. By fitting the profiles to the formula I(t)=A.sub.1 e(-t/.tau..sub.1)+A.sub.2 e(-t/.tau..sub.2) one can quantify the differences between tissues of various conditions. For example, non-malignant human breast tissues exhibit a slow component (.tau..sub.2) which is less than 1.6 ns whereas malignant human breast tissues exhibit a slow component (.tau..sub.2) which is greater than 1.6 ns. In addition, non-malignant human breast tissues exhibit a ratio of fast to slow amplitudes (A.sub.1 /A.sub.2) which is greater than 0.