We simultaneously measured the H/M atomic ratio and the magnetization, M, of LaNi5–H while it was activated and then cycled many times, at 100 °C and then 26 °C. The overall magnetization of the sample rose steadily as cycling precipitated Ni. In addition, however, M exhibits a large degree of magnetic hysteresis between the absorption and desorption isotherms. The magnetization in both the pure α and β phases is very sensitive to the H concentration. Furthermore, we found that the intrusion of the intermediate γ phase, LaNi5H≈3, also profoundly altered the magnetic properties of the sample. It is proposed that the ferromagnetism occurs by exchange between clusters of fcc Ni spins, via polarization of the conduction electrons.