Quantachrome Instruments, Boynton Beach, Fla., introduced a new method for the characterization of micro- and mesoporous materials, including catalysts, separation membranes, sensors and other zeolite-based systems. The method is based on Nonlocal Density Functional Theory (NLDFT) and is designed for pore size characterization of zeolite materials (including MCM-41) with cylindrical pores using high-resolution, low-pressure argon absorption isotherms at 87.3 K. In contrast to the widely used classical, macroscopic theories and models, the new method is microscopic in a sense that it describes the sorption and phase behavior of Ar in a narrow pore on a molecular level. This leads to a much more accurate pore size analysis for materials consisting of narrow micropores and mesopores in a diameter range from 0.5 nm up to ca. 20 nm.