Elastic recoil detection (ERD) analysis is successfully applied to in situ measurements of hydrogen isotope distributions formed in palladium and titanium during deuterium ion implantation to observe phenomena connected with so-called cold fusion. In situ analysis is shown to be effective in identifying the physical processes occurring in such hydrogen-metal systems. The system is equipped with charged-particle detectors not only for the detection of nuclear reaction products occurring under bombardment with kilo-electron-volt deuterium ions but also for ERD analyses using a mega-electron-volt accelerator. The beam-target D(d,p)t reaction yield during implantation is dependent on the beam current or the deuterium flux. This is interpreted in terms of a temperature dependence of the deuterium concentration that is measured in situ by the ERD method. During the bombardment with heavy ions for ERD, measurements of reaction products are also made simultaneously with those of the recoil particles to clarify the structure of the spectra, although some unidentified peaks remain.