Living systems provide metal sites with properties which cannot yet, in many cases, be reproduced in man-made molecular structures. Among these metal sites are those involved in biologically-essential electron transfer processes, such as cellular respiration and photosynthesis. While it would be difficult to overestimate the value of X-ray diffraction in arriving at three-dimensional models of macromolecules, the resolution provided by the X-ray method applied to protein crystals does not approach the 0.1A detail required to describe and understand electronic structure and processes. Spectroscopic methods are needed. In Professor Brill's laboratory magnetic and optical techniques are employed to study the interactions of metal ions, especially copper and iron,with proteins. There is new physics to be learned from such studies of metal-protein sites, principles that can be related to biological function. Quantum mechanical models, incorporating the effects of low symmetry and electron delocalization, are being developed in the Brill laboratory to provide a unified electronic structural basis for magnetic, optical, and magneto-optical data taken together. Lineshape and spin relaxation effects are used here to characterize energy level and structural distributions, and to quantify torsional force constants at active sites, information now recognized as essential for the understanding of protein function.