The relaxation times for electron scattering (Dingle temperatures) and the concentration dependence of extremal cross-sectional areas A of the Fermi surface of dilute palladium-tritium alloys (PdT_x with 0<or=x<or=0.0011) are obtained from the de Haas-van Alphen experiments in fields up to 11 T at temperatures down to 1.4K. The relative changes in extremal cross-sectional areas of the Fermi surface d ln A/dx induced by tritium in Pd are 0.31 for the (001) orbit on the Gamma centred electron sheet, -2.5 for orbits on the X-hole pockets and -11 for the L-hole pocket. Furthermore, for the first time the concentration dependence of one of the extremal cross-sectional areas of the fifth band jungle gym is measured in dilute palladium-hydrogen and palladium-deuterium alloys. The results of these experiments show that the intriguing isotope effects observed previously are confined to states on the hole ellipsoids at points X and L of the Brillouin zone. As the density of states associated with these Fermi surface sheets represents only 3% of the total density of states at the Fermi energy, isotope effects in macroscopic quantities such as magnetic susceptibility and electronic specific heat are too small to be observed. This is in agreement with recent measurements by Blaurock (1983) and Wicke (1984).