Guest-induced transitions from alpha and gamma phases of syndiotactic polystyrene (s-PS) toward cocrystalline and nanoporous phases, and related guest-induced orientation phenomena, have been investigated by X-ray diffraction. Guests, being able to induce cocrystal formation in amorphous s-PS samples, are able to induce room-temperature cocrystal formation from gamma and alpha form films, only if their vapor pressure is higher than 20 and 60 Torr, respectively. Guest-induced recrystallizations of unoriented gamma form films generally lead to unoriented cocrystalline and delta form films, while chloroform-induced recrystallization leads to cocrystalline and epsilon form films with perpendicular orientation of chain axes. On the other hand, guest-induced recrystallizations of unoriented alpha form films generally lead to oriented cocrystalline and derived delta form films. In particular, recrystallizations of unoriented alpha form films by room-temperature sorption of trichloroethylene and CHCl3 lead to films with (002) uniplanar and (<(2) over bar>10) uniplanar orientations, i.e., with chain axes perpendicular and parallel to the film plane, respectively. The new procedures to prepare nanoporous films with different uniplanar orientations present substantial advantages with respect to the procedures already described in the literature.