Communication: Lasing in conjugated polymer thin films? Not so, according to the results presented here. As previously reported, for films of a variety of conjugated polymers on glass substrates the emission spectrum narrows with increasing optical-pump intensity when pulsed excitation is used. A detailed study is described here of this spectral narrowing phenomenon using films of poly(p-phenylenevinylene) (PPV). Evidence is presented that weakens the case for lasing being the mechanism involved and supports amplification of spontaneous emission by waveguiding.