The results of spectral studies of iron(II) protopor-phyrin IX and iron(II) hematoporphyrin IX with several substituted pyridines are reported. The existence in solution of an iron(II) porphyrin complex coordinated to a water molecule and to a substituted pyridine was shown by isolation of the complex from solution. The complex isolated was dimeric inono-4,4′-dipyridyl diaquo iron(II) hematoporphyrin. Addition of ethanol to the aqueous solvent inhibits coordination of iron(II) porphyrins with substituted pyridines. The protoporphyrin ring enhances coordination relative to the hematoporphyrin ring.