We report a detailed study of the gain properties of three polyfluorenes: poly(9,9-dioctylfluorene-co-9,9-di(4-methoxyphenyl)fluorene (F8DP), poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT), and a Dow proprietary copolymer, Dow Red F. The emission spectra of these conjugated polymers span the full visible spectrum from 400 to 800nm. We observe amplified spontaneous emission (ASE) with peak wavelengths at 452, 576 and 685nm for F8DP, F8BT and Red F, respectively. Low stimulated emission thresholds in the region of 0.1-0.45 μ J per pulse are demonstrated for planar asymmetric waveguides. Variable stripe length gain measurements at the peak ASE wavelengths show large net gains up to 66cm-1. Very low loss coefficients, in the range of 3.2-14.8cm-1, were also found. © 2003 Elsevier Science B.V. All rights reserved.