The solution conformation of bovine anaphylatoxin C5a has been investigated by nuclear magnetic resonance (NMR) spectroscopy. The 1H-NMR spectrum is assigned in a sequential manner using a variety of two-dimensional NMR techniques. A qualitative interpretation of the short range nuclear Overhauser enhancement data involving the NH, C alpha H and C beta H protons suggests that C5a has four helices comprising residues 5-11, 15-25, 33-39 and 46-61, and is composed of a globular head (residues 5-61) and a C-terminal tail. The polypeptide fold was determined by hybrid distance geometry-dynamical simulated annealing calculations on the basis of 203 approximate interproton distance restraints, 22 distance restraints for 11 intrahelical hydrogen bonds (identified on the basis of the pattern of short range NOEs and slowly exchanging backbone amide protons) and restraints for the 3 disulfide bridges. The overall polypeptide fold is similar to that of the sequence related human recombinant anaphylatoxin C5a [(1988) Proteins 3, 139-145].