The present work is an extension of the infrared absorption measurements by Boggs and Welsh on the quantum diffusion of o-H2 molecules in almost pure p-H2 solid. The new data, combined with the earlier data, were analyzed statistically. The rate constant which characterizes the formation of o-H2 molecular pairs was found to be in the range 0.3–0.7 h−1 for ortho concentrations of 0.7–1.8% and temperatures from 1.14 to 2.10 K. The results show reasonable agreement with the theory of Oyarzún and Van Kranendonk.