Whereas it has been recognized for some time that the absorption of sound in suspensions of erythrocytes is primarily a macromolecular phenomenon, recent observations have led us to believe that interactions between macromolecules may play a significant role as well. Two tests of the interaction postulate are reported: (i) Acrolein or glutaraldehyde fixing of bovine erythrocytes, which cross‐links macromolecular hydrophobic groups, causes an increase in specific absorption by as much as a factor of five at 30 MHz. The absorption increase is greatest at 30 MHz and above. (ii) Suspension of fixed erythrocytes in low‐dielectric constant liquids (ethylene glycol and ethanol), thus increasing forces between ionic groups, further increases the specific absorption by as much as a factor of four at 10 MHz. The absorption increase associated with solvent changes is greatest at 10 MHz and below. Scattering, viscous relative motion, and thermal absorption have been ruled out as explanations for the observations. The explanation is more apt to lie in some forms of chemical or structural relaxations.