The picosecond NO geminate rebinding kinetics of wild-type leghemoglobin, a monomeric plant hemoglobin with structural similarity to myoglobin, and six mutant proteins at the distal histidine (H61G, H61A, H61V, H61L, H61R, H61F) are investigated. All of the mutant proteins yield rebinding kinetics that are initially more rapid than that of the wild-type protein. At long times, the rebinding of H61F becomes slower than that of wild-type leghemoglobin. The H61V, H61L, and H61G mutant proteins give extraordinarily rapid and complete geminate rebinding. On a 40 ps time scale, distal effects are overwhelmingly evident for all of the mutants considered. That binding is both rapid and, in several cases, essentially single-exponential is suggestive of the nature of the barrier induced by the distal modification: it must be such that the ligand is prohibited from reorienting with respect to, and diffusing sufficiently far from, the heme iron so that a distribution of return paths is not offered to it. Over the past 20 years, the relative importance attributed to the proximal and the distal sides in modulating geminate ligand binding has varied considerably. Our results with leghemoglobin are discussed in terms of the relative contributions of proximal and distal effects to geminate rebinding kinetics.