We report a study of the amplified spontaneous emission (ASE) in highly oriented films of dioctyl substituted polyfluorene (PFO). We demonstrate amplification of blue light via ASE measurements on optically pumped aligned PFO planar asymmetric waveguides and investigate the influence that the orientation of the polymer chains has on its properties as an amplifying medium. We show that the threshold energy for ASE and the intensity of the emitted amplified radiation is dependent on the excitation polarization, chain alignment axis and excitation geometry and propose specific optimised excitation configurations for low threshold, efficient ASE. Identical measurements are performed on isotropic PFO films for comparison.