The equilibrium thermodynamics of confined linear homopolymers between two impenetrable walls was investigated by means of Monte Carlo simulations in the canonical ensemble with the parallel tempering algorithm. The influence of confinement and chain size on the potential energy, heat capacity, radius of gyration, and the end-to-end distance was investigated as a function of temperature. A bead-spring model was used to simulate the chains. Two conformational changes were observed regardless of the differences in confinement of chain size: The coil-to-globule transition that resembles the gas to liquid transition and the liquidlike to solidlike transition. An additional transition between solid states was also observed for the smallest chain size studied (16 beads). Results indicate a shift of the coil-to-globule transition temperature to lower values as the slit width approaches the two-dimensional case (wall separation equal to bead diameter), and to higher temperature regions as the chain length increases. For separations greater than five bead diameters, the thermodynamic behavior was similar to the behavior in unconfined space. (C) 2003 American Institute of Physics.