The hydrogen content in aerosol particles of a-Si:H, forming during pyrolysis of silane, is studied by means of the methods of hydrogen evolution and IR spectroscopy. The conclusion is drawn that the evolution peaks at 650, 730, and 750 to 850 K correspond to hydrogen present in the dihydride groups of polysilane chains, the monohydride groups of the clustered phase, and the monohydride groups of the dilute phase, respectively. In the IR spectra the monohydride groups of the clustered phase cause absorption near 2000 cm(-1) and the monohydride groups of the dilute phase near 2100 cm(-1). Under low silane conversion the main fraction of hydrogen is contained in (SiH2)(n), under conversion more than 50% in monohydride groups.