Nonphotochemical hole burning (NPHB) and femtosecond pump-probe experiments have previously shown that following their excitation, the B800 molecules of the LH2 complex of Rhodobacter sphaeroides and Rhodopseudomonas (Rps.) acidophila relax by two channels. The decay channel observed for excitation on the low energy side of the B800 absorption band is due to B800 --> B850 excitation energy transfer which occurs in similar to2 ps at 4 K. The additional decay channel becomes detectable for excitation on the high energy side of the B800 band. The mechanisms that have been proposed for this channel are: (i) vibrational relaxation following excitation of vibronic levels associated with the Qy-states of either the B800 or B850 bacteriochlorophyll a molecules; (ii) direct excitation of upper B850 exciton levels, followed by downward relaxation within the B850 manifold; (iii) intraband B800-B800 energy transfer involving only the B800 molecules; and (iv) downward energy transfer of initially excited mixed B800-B850 states. Presented here are NPHB results for intact LH2 and B800-deficient LH2 complexes of Rps. acidophila (strain 10050). The latter contain only one B800 molecule, rather than nine. In sharp contrast with the intact LH2 complex, the zero-phonon holewidths for the B800-deficient LH2 complex were observed to be independent of the location of the burn frequency within the B800 band, 3.2 +/- 0.3 cm(-1) at 4 K. This finding and others eliminate the first two of the above mechanisms. It is argued that the third mechanism is highly unlikely. It is proposed that mixed B800-B850 states are mainly responsible for the additional decay channel. These mixed states could undergo downward relaxation to B800 levels that are mainly "B800" in character and to levels that are mainly "B850" in character.