G. A. Turnbull, P. Andrew, M. J. Jory, William L. Barnes, and I. D. W. Samuel, Physical Review B, Vol. 64, article 125122 (2001). "Copyright © 2001 by the American Physical Society." ; We present an experimental study of the emission characteristics and photonic band structure of a distributed feedback polymer laser, based on the material poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene]. We use measurements of the photonic band dispersion to explain how the substrate microstructure modifies both spontaneous and stimulated emission. The lasing structure exhibits a one-dimensional photonic band gap around 610 nm, with lasing occurring at one of the two associated band edges. The band edge (frequency) selection mechanism is found to be a difference in the level of output coupling of the modes associated with the two band edges. This is a feature of the second-order distributed feedback mechanism we have employed and is clearly evident in the measured photonic band structure