The lasing performance and wavelength tunability of a novel high efficiency copolymer poly[(2,5,2",5"-tetraoctyl)-p-terphenyl-4,4"-ylene vinylene-p-phenylene vinylene], TOP-PPV, pumped with third harmonic radiation of a Nd:YAG laser, was studied in various organic solvents. The results were compared with Coumarin 120 and Coumarin 47 in ethanol under identical experimental conditions. The efficiency of the TOP-PPV copolymer in hexane exceeds that of both coumarin dyes with more than 50%. The laser emission of the polymer dye in hexane is tunable in the wavelength region between 414 and 456 nm (Δλ=38 nm).