Density functional calculations are used to calculate the electronic structure of the bacteriopheophytin a radical anion, phi(A) formed in the initial electron-transfer reactions of bacterial photosynthesis. Using the hybrid B3LYP functional together with the double zeta basis set EPR-II, C-13, H-1, O-17 and N-14 isotropic and anisotropic hyperfine couplings are calculated and explained by reference to the electron density of the highest occupied molecular orbital and of the unpaired spin distribution around the radical. Good agreement is observed between calculated and experimental hyperfine couplings. Hydrogen bonding to the carbonyl group of ring E leads to minor changes in the unpaired spin density distribution and the resultant hyperfine couplings. The electronic structure of the anion radical form of the other bacteriopheophytin a molecule, phi(B), found along the inactive-electron-transfer (B) branch, is also studied, and the calculated electronic properties are compared with phi(A) It is shown that, whereas the electron density of the SOMO of the phi(A) radical is delocalized along the acetyl group attached to the A ring, this delocalization is much reduced for the phi(B) radical. The implication of this finding for selective electron transfer along the A branch is discussed.