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1H NMR spectroscopy and solution structure computations have been used to examine ferrocytochrome c-551 from Pseudomonas stutzeri (ATCC 17588). Resonance assignments are proposed for all main-chain and most side-chain protons. Distance constraints were determined on the basis of nuclear Overhauser enhancements between pairs of protons. Dihedral angle constraints were determined from estimates of scaler coupling constants. Twenty-four structures were calculated by distance geometry and refined by energy minimization and simulated annealing on the basis of 1033 interproton distance and 57 torsion angle constraints. Both the main-chain and side-chain atoms are well defined except for a loop region around residues 34-40, the first two residues at the N-terminus and the last two at the C-terminus, and some side chains located on the molecular surface. The average root mean squared deviation in position for equivalent atoms between the 24 individual structures and the mean structure obtained by averaging their coordinates is 0.54 +/- 0.08 A for the main-chain atoms and 0.97 +/- 0.09 A for all non-hydrogen atoms of residues 3-80 plus the heme group. These structures were compared to the X-ray crystallographic structure of an analogous protein, cytochrome c-551 from Pseudomonas aeruginosa [Matsuura, Takano, & Dickerson (1982) J. Mol. Biol. 156, 389-409). The main-chain folding patterns are very consistent, but there are some differences. The largest difference is in a surface loop segment from residues 34 to 40.