Porphyrin manganese complexes are of interest, both from their possible involvement in oxygen formation in photosynthesis and as analogues to the biologically important iron porphyrin complexes. Recent studies by Bocher(1–3) have indicated that porphyrin manganese III complexes exhibit a unique absorption spectrum indicative of an unusual electronic structure. Their spectra are considerably more complex than other metalloporphyrins, e.g., heme proteins, which typically exhibit visible absorption spectra containing two prominent bands (α,β) in the 16 to 20-kK region and a third, more intense band, the Soret band, at 23 to 25 kK.