Abstract Raman spectroscopy is a laser-based analytical technique that enables chemical characterization of molecules in a sample. It is based on the inelastic scattering of photons by molecular bond vibrations. A Raman spectrum obtained from single cells is an intrinsic molecular fingerprint of the sample, revealing detailed information about DNA, RNA, protein, lipid, and carbohydrate content as well as macromolecular conformations. This technique is rapid, non-invasive and non-destructive. We have demonstrated that single-cell laser tweezers Raman spectroscopy (LTRS) reliably discriminates between normal human T- and B-lymphocytes and their transformed, Jurkat-T and Raji-B, counterparts. Herein the same technique is used to discern normal human T- and B-cells from T- and preB-leukemia cells. Also, demonstrated are Raman spectra changes that result from the activation of normal T-cells with a combination of TPA and ionomycin, and normal B-cells by cross linkage of surface immunoglobulin. T- and B-cells were isolated from healthy volunteers. T- and preB-leukemia cells were isolated from patient samples. Spectra are both compared directly and analyzed by principal component analysis. Significant Raman spectra differences in characteristic DNA and protein signals discriminate between normal cells and their leukemia counterparts. Human leukemia cells were indistinguishable from Jurkat-T and Raji-B cells. Changes in spectra that result from cell activation and proliferation only partially account for the spectra changes of leukemia cells. These data demonstrate the utility of LTRS to discern normal lymphocytes from both transformed cells and leukemia cells.