A published method previously developed to measure the swelling characteristics of powdered coal samples has been adapted for swelling measurements on various peat, pollen, chitin, and cellulose samples. The swelling of these macromolecular materials is the volumetric manifestation of absorption, that is, sorption by dissolution (or partitioning) of the sorbed liquids into cross-linked macromolecular solid phases. Direct evidence for the existence of this additional category of sorbed materials has been obtained for soil organic materials by the present research; however, it seems to be limited by molecular size-exclusion effects to fairly small molecules. Liquids with molar volumes greater than about 93 cu m/mol appeared to be strongly excluded from sorption inside most cross-linked soil organic materials studied in this work. Cellulose excluded liquids with molar volumes greater than about 88 cu m/mol. (Copyright (c) 1993 SETAC).