[en] The hydrogen sorption properties of the Lasub(1-x)Casub(x)Ni₅ and La(Nisub(1-x)Cusub(x))₅ systems were investigated at various temperatures and at pressures up to 20 atm. It was found that initial substitution of La by Ca in LaNi₅ caused an increase in the hydrogen dissociation pressure, up to Casub(0.3)Lasub(0.7)Ni₅. In the Casub(0.3)Lasub(0.7)Ni₅-CaNi₅ range, the dissociation pressure decreased. The absorption capacity of CaNi₅ was dependent on the purity of the sample and increased significantly at low temperatures. The stability of La(Nisub(1-x)Cusub(x))₅ hydrides increased linearly from LaNi₅ to LaCu₅. These features are discussed in the light of existing models of ternary and pseudoternary hydride stability. Finally, the role of the measured change in entropy ΔS in determining the occupied interstitial sites in the hydride is outlined and discussed in relation to these systems. (Auth.)