ABSTRACT Acute Lymphoblastic Leukemia (ALL) accounts for majority of the childhood leukemia. Outcome of children with ALL treatment has improved dramatically. Sensitive techniques are available today for detection of minimal residual disease in children with ALL, which provide insight into the effective cytotoxic treatment. Here, we present a case study, where lymphocytes isolated from two children before and after the treatment were characterized using microscopic Fourier Transform Infrared spectroscopy. Significant changes in the absorbance and spectral pattern in the wavenumber region between 800-1800 cm -1 were found after the treatment. Preliminary analysis of the spectra revealed that the protein content decreased in the T-type ALL patient before the treatment in comparison to the age matched controls. The chemotherapy treatment resulted in decreased nucleic acids, total carbohydrates and cholesterol contents to a remarkable extent in both B and T-type ALL patients