[en] In a finite beta (β = 8πn₀kT₀/B₀²) plasma, where the plasma pressure n₀kT₀ is an appreciable fraction of the confining magnetic field energy-density B₀²/8π, density-gradient driven drift waves couple with Alfven waves when the phase velocities of the two waves become comparable. The resulting hydromagnetic drift-Alfven waves separate into two branches--a drift mode and an Alfven mode, with both modes exhibiting magnetic field and localized density fluctuations near the coupling point. The dispersion relation of the collisional drift-Alfven wave is derived by using a slab-geometry, two-fluid model which includes finite beta, electron-ion collisions, ion-ion collisions, finite ion larmar radius, temperature fluctuations, and an axial electron current. A hydromagnetic drift mode is found to be unstable in a moderately dense plasma. A localized ''Alfven'' mode is destabilized only with the passage of an axial current along the plasma column. In order to check the theoretical predictions an experiment is performed in a finite-beta plasma of density n₀ = 10¹³-10¹⁵ cm^-3 and temperature T/sub e/ approximately T/sub i/ = 1-7 eV. (U.S.)