The coupled equations of motion for linearly interacting elastic foam and saturating fluid are formulated and solved for excitation at fixed frequency and wave number. As known from previous work on porous media, the longitudinal waves in the foam and fluid are coupled, and the shear wave in the foam is modified while imparting rotational motion to the fluid. Resulting fields are expressed suitably for use in situations of axisymmetry. The characteristic equation for free waves and relations between field coefficients are given explicitly for propagation within a rigid tube. Acoustically, a characteristic feature of the application to liquid‐saturated foam is the high mass porosity and compressibility of the empty foam, commending a corresponding limiting approximation. Applied to propagation in a rigid tube, this yields a modification of of the acoustic wave speed and impedance due to foam that is measured by (sQ)1/2(ωa/ct)−1, whereQ=iΔ/(1+iΔ), Δ is a drag‐interaction coefficient,sthe ratio of the mass of foam to that of fluid,athe tube radius, andctthe shear‐wave speed of empty foam. The interaction effect thus exhibits saturation, sinceQbecomes independent of Δ for sufficiently strong interaction. In a contrary limit where the foam is nearly stationary, the effect of foam is measured rather by Δ. Poiseuille flow in the presence of foam is also treated. The hydrodynamic determination of Δ is carried through for idealized foam geometries. In the viscous domain where the viscous depth exceeds the filament diameter, Δ is real and varies as ν/ωD2, whereDis pore size, with coefficient weakly dependent on porosity. At high frequencies Δ becomes negative imaginary on account of the induced‐mass effect.