The tripeptide l-alpha-acetyl lysyl-l-alanyl-l-phenylalanine methyl ester is being used as a paradigm of the visual protein opsin, to gain insight into the visual process, especially with regard to the origin and interpretation of the 500 nanometer absorption peak in rhodopsin. We feel that this peak arises from a charge-transfer interaction between the retinene chain and the phenyl ring. Retinene is known to form several complexes interpretable as charge transfer and one finding is that the reaction of retinene with antimony trichloride results in sufficient unpairing of an electron to an ESR signal. Retinal reacts with this tripeptide to parallel its spectral activity with phospholipids and perhaps opsin. An absorption at 480 nanometers may be equivalent to the 500 nanometer peak in rhodopsin and be a charge transfer band. Spectral, optical rotatory dispersion and circular dichroism investigations have been made. A program for calculating molecular geometries by the strain energy minimization method has been finally debugged. Since in its original form this program handled only carbon, hydrogen and oxygen, it was necessary to calculate many more additional parameters (bond moments, bending force constants, etc.) involving atoms and bonds important in biologically active molecules.