E le c tric v x f dissociation of H ions moving through a magnetic fie ld has been measured for e le c tric fie ld strengths near 2 MV/cm. The H ions were obtained by charge exchange of protons in water vapour and were accelerated to 49.5 MeV by the proton linear accel erator at the Rutherford High Energy Laboratory. Stripped particles were detected using an acoustic spark-chamber. Experimental lifetim es are lower by approximately a factor of two from those predicted by Mullen and a factor of three from those predicted by Hiskes Our measurements also appear inconsistent with those of Cahill et dl. 3)