Adsorption isotherms of Ar and CH4 were used to study the suitability of boron carbide as substrate for physisorption. Samples from three different groups of boron carbide were used. The samples were subjected to different cleaning treatments. The best results were obtained on powders and on whiskers heated to 1770 degrees C in a N-2 atmosphere. There are four resolvable steps in multilayer adsorption isotherm data measured on these high-temperature-treated substrates. Detailed monolayer adsorption data measured at 77.3 K for CH4 on these samples reveal the presence of a substep near monolayer completion. This feature is probably related to a solidification transition in the monolayer as the coverage is increased. The specific surface areas of the boron carbide samples used range between 0.3 and 0.15 m(2)/g. Our results indicate that boron carbide can, when cleaned at sufficiently high temperatures, result in a suitable substrate for physisorption studies.