The biochemical composition of normal human brain tissue in comparison with that of brain-tumour tissue was studied and diagnosed by means of the attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy technique. IR spectroscopy is a potential histopathological tool for detecting and diagnosing cancer and other diseases. In the study, the amounts of lipids, protein, and water in different brain-tissue specimens from patients of various ages were determined from their ATR-FTIR spectra upon analysing a combination of the pure-component spectra. A higher level of biocomponents was observed in the normal tissue, and in particular, more fluid (water) was contained in benign tumours. The age of patients was found to play an important role; patient age exhibited a direct correlation with the concentration of biocomponents, with increasing age corresponding to a reduction in lipids and proteins. These results demonstrate the diagnostic potential of ATR-FTIR spectroscopy for evaluating brain tumours in terms of its ability to distinguish between normal tissue and tumours in vivo and afford real-time intraoperative diagnosis.