We report the results of a study on microcavity structures containing the conjugated polymer poly(2,5-dialkoxy-p-phenylenevinylene). Strong spectral narrowing, from a full width at half-maximum (FWHM) of 128 to 16 nm for photoluminescence (PL) and 112 to 35 nm for electroluminescence (EL) is observed. Modification of the cavity path length is used to produce a shift in the PL peak emission wavelength by 50 nm. In addition, we show that the EL emission wavelength has a clear angular dependence that can be described using a transfer-matrix reflectivity (TMR) model. These are characteristic signatures of the modification of spontaneous emission properties through coupling to resonant cavity modes.