Amino acid solutions have absorptions which are generally small compared to those for proteins. Proteolytic enzyme treatment of proteins in solution reduces their absorption. These observations suggest that absorption increases with molecular weight. However, measurements of sugars, polysaccharides, amino acids, and proteins yield no correlations of absorption with molecular weight within these groups. Therefore, it is concluded that absorption increases in these molecules with increasing molecular weight only in a threshold sense, with absorption increasing significantly only in a restricted molecular weight range. This range may approximate that observed for polyethylene glycol and dextran, viz., 1 to 100 monomer units. However, there is some indication that the transition range may be narrower than a factor of 100 in molecular weight.