Results from the first Stark hole-burning spectroscopic studies of photosynthetic complexes are reported. External electric field effects were determined as a function of laser burn frequency and polarization for the B800 band and the B870 band of Rhodobacter sphaeroides, where B870 is the lowest exciton level of the strongly coupled bacteriochlorophylla molecules of the B850 ring. For either parallel or perpendicular polarization of the burn laser relative to the external Stark field, only broadening of the zero-phonon holes which is linear in field strength was observed. Near the center of the B870 and B800 bands, f(Δμ ,Δμ )=(1.1,1.4) and (1.1,0.8) Debye, respectively, where f is the local field correction factor. However, a dependence of the Δμ-values on location of the hole within the inhomogeneously broadened absorption bands is observed. For B870 they increase by 10-20% from the blue to red edge while for B800 an opposite trend is observed. Results for B870 of Rhodopseudomonas acidophila and Rhodospirillum molischianum are similar. A detailed discussion of the results and a comparison of them with those from classical Stark modulation spectroscopic studies of the entire B800 and B850 absorption bands are given. It is concluded for the B850 ring that mixing of charge transfer states with the Q y -exciton levels is of minor importance. The hole burning data, together with consideration of the C n -symmetry and the effects of energy disorder from structural heterogeneity, suggest that localization effects from energy disorder are probably important for understanding the effects of external electric field on the B850 band which is comprised of several components.