Electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopy are used to study reducibility and adsorbate interaction of Ti in titanosilicate TS-1 molecular sieve. Various reduction methods were used to reduce Ti(IV) in TS-1 to Ti(III) which was then monitored by ESR, When TS-1, after dehydration and oxygen treatment at high temperature followed by evacuation (activation), is gamma-irradiated at 77 K; an ESR signal with g perpendicular to = 1.970 and g perpendicular to = 1.906 is observed for isolated Ti(III) centers. Radiation induced defect centers known as V centers are also observed after gamma-irradiation. When activated TS-1 is treated with CO or H-2 at 673 K, an axial ESR signal with g perpendicular to = 1.968 and g parallel to = 1.933 is observed which is suggested to be Ti(III)(CO)(n) and TiO(III)(H-2)(n) complexes. When activated TS-1 is exposed to D2O at room temperature and subsequently gamma-irradiated at 77 K, a new ESR signal with g = 1.924 is observed. This species is identified as Ti(III)-(OD)(1) from D-2 ESEM data. Adsorption of CH3OD on activated TS-1 produces a new Ti(III) species with g = 1.931. This species is identified as Ti(III)-(CH3OD)(1) from D-2 ESEM data. Adsorption of C2D4 on activated TS-1 produces a new Ti(III) species with g perpendicular to = 1.968 and g parallel to = 1.910. This species is identified as Ti(III)-(C2D4)(1) from 2D ESEM data. Possible coordination geometries of the various Ti(III)-adsorbate complexes are discussed.