Abstract : We consider the simple one-pion exchange (Yukawa potential) contribution to the 2S hyperfine splitting in muonic hydrogen which had, until recently, been disregarded. We evaluate the relevant vertex amplitudes, in particular $\pi^0\mu^+\mu^-$, combining low energy chiral expansions together with experimental data on $\pi^0$ and $\eta$ decays. The result for the 2S HFS is found to be small but not irrelevant.
