Lasing is reported at the edge and in the middle of the selective reflection band produced in the visible region of the spectrum for the cholesteric phase of a lyotropic liquid crystal formed from an optically active polyisocyanate in toluene. This is the first observation of lasing from a stiff polymer based lyotropic liquid crystal. Lasing was observed at a relatively low threshold when the selective reflection band overlaps with the emission peak of an incorporated dye molecule. The absence of fine structure of the selective reflection band at wavelengths near the edge of this band indicates that the cholesteric liquid crystal is not perfectly periodic. Lasing in these multidomain films may therefore be associated with defects in the periodic structure.