The primary photochemistry of the (M)L214H and (M)L214H/(L)E104V mutant bacterial reaction centers (RCs) from Rhodobacter sphaeroides has been investigated at room and cryogenic temperatures. In both mutants the native bacteriopheophytin electron acceptor (BPh(L)) is replaced with a bacteriochlorophyll (BChl) molecule denoted by beta; in the double mutant a hydrogen-bonding interaction of beta is removed. The initial stage of charge separation, formation of an intermediate P+I-, is slowed somewhat in both mutants but without a detectable loss in yield. However, the yield of the subsequent stage of charge separation, P+I- --> P(+)QA(-), is significantly reduced due to the combination of slower electron transfer from I- to Q(A) and enhanced charge recombination of P+I- to the ground state. For example, in the double mutant the inherent time constant for electron transfer at 285 K is lengthened 10-fold to similar to 2 ns and the inherent time constant for charge recombination is reduced 20-fold to similar to 750 ps, giving a p(+)Q(A)(-) yield of 27%. At 77 K, in both beta-containing RCs electron transfer from I- to Q(A) is slowed and the p(+)Q(A)(-) yield reduced compared to the value at 285 K.