Phase separation of binary liquids with an upper critical temperature in porous materials is studied by H-1 NMR cryoporometry and cross-relaxation spectroscopy and by N-15 NMR spectroscopy. The first method provides domain size distributions of the separating minority component while the other ones verify the segregation of the two liquids on molecular level. We find that metastable structures are formed manifested by bimodal domain size distributions. The kinetic arrest of domain growth may be imposed upon by bottlenecks in the porous structure that block diffusion of entire droplets. Practical applications, if one of the liquid components is polymerized, include mobile polymer particles trapped in porous matrix that can serve, e.g., as filters with microscopically amphiphilic pathways. (C) 2003 Elsevier B.V. All rights reserved.