The reactivity of hydrogen towards the lanthanum silicides, La5Si3. LaSi and LaSi2, has been studied by gravimetric and differential thermoanalytical methods. Synthesized silicides and hydrogenated phases have been characterized by X-ray diffraction. The hydrogen interaction is attributed to the lanthanum content of the silicide phase. Whereas LaSi2 does not react with hydrogen over a wide pressure-temperature range. La5Si3 takes up hydrogen even at 100 degreesC. Hydrogenation of La5Si3 leads from a metastable hydride with about one hydrogen atom per lanthanum atom to the decomposition into lanthanum hydride, LaH2+x and another phase without X-ray pattern. On the contrary, hydrogen release is not complete at temperatures up to 900 degreesC. LaSi reacts reversibly with hydrogen under formation of a ternary hydride phase.