Tunability of the cw radiation from a GaAs injection laser in an external dispersive cavity was achieved over a range of 150 Å about a center wavelength of 8525 Å at 77°K. The emitted radiation was analyzed with a Fabry-Perot etalon. Under certain conditions single-mode operation with cw output power as large as 17 mW was observed. Half-width of such modes was estimated to be less than 350 MHz. © 1972 The American Institute of Physics.