A method for recording infra red spectra from frozen dried tissue sections is descr. Infra red spectra of neural tissue (cerebellum, hippocampus, tectum, diencephalon, grey matter, white matter, sciatic nerve, and optic nerve) and visceral tissue (liver, heart, medulla and cortex of the kidney, adrenal, thymus, and spleen) obtained from rabbits, dogs, and human postmortem material are descr. All the infra red tissue spectra show the known "polyamide vibrations" between 3.04 and 6.88[mu], an unassigned band at 8.06u, and a fingerprint region from 11-8u. The tissue spectra in the finger-print region are characteristic for the individual organs. Neural tissue of different origin (rabbit, men, dog, frog) show similar spectra. Assignment of tissue spectra to chemical compounds as nucleic acid derivatives is discussed. A method for quantitative infra red spectroscopy in brain is descr. in which the "polyamide band" at 6.44u. was used as internal standard. Significant spectroscopic changes in brain tissue of animals in insulin shock have been demonstrated.