Interference microscopy is applied to carry out investigations of the influence of the regular intergrowth effects commonly observed in large silicalite-1 crystals on adsorption/desorption of isobutane. The intracrystalline concentration profiles measured by interference microscopy during adsorption of isobutane are compared with those simulated using the Monte Carlo method. The comparison of the simulated and the measured profiles allows the possibility that the uptake of isobutane from the gas phase into silicalite-1 crystals proceeds through the internal interfaces separating the intergrowth sections of the crystals to be ruled out. The diffusion coefficient of isobutane obtained by comparing the simulated and the measured concentration profiles is found to be in agreement with the previously reported diffusivities of isobutane in silicalite-1.