The NO, N-methylimidazole complex of isotopically enriched octaethylporphyrinatoiron(III) chloride, [OEP57Fe(NO)(N-MeIm)]+C1- has been prepared in dimethylacetamide solution and studied by low-temperature Mössbauer spectroscopy in the presence and absence of a magnetic field. This complex is a model for the Fe(III)-NO complexes of the nitrophorins of the blood-sucking insect, Rhodnius prolixus, where NO is released from the histidine-coordinated ferrihemin center of each of the proteins upon the insect's injection of the saliva into the victim. The [OEPFe(NO)(N-MeIm)]+C1- complex is EPR silent and behaves as a diamagnetic species, with quadrupole splitting ΔEQ = 1.64 mm s-1, asymmetry parameter η = 0.4, isomer shift δ = 0.02 mm s-1, and linewidth Γ= 0.3 mm s-1. Two electron configurations, Fe(III)-NO (low-spin d5, strongly antiferromagnetically coupled to NO), or Fe(II)-NO+ (low-spin d6, purely diamagnetic), are possible. Which is the actual configuration cannot be determined until detailed molecular calculations are carried out. The low-spin OEPFe(III)-bis-N-methylimidazole complex also present in this sample has EPR g-values, quadrupole splitting, isomer shift, and hyperfine splittings typical of rhombic low-spin ferriheme centers.