We have synthesised and investigated poly(3-dodecylthiophene), P3DT, with the side-chains in regioregular head-to-tail positions. The content of head-to-tail linked units in the polymer is assessed by NMR spectroscopy and estimated to above 95%. This regioregular P3DT shows more structure in the optical absorption spectra than the regiorandom material. Mobile dopants/impurities are present in a concentration of the order of 10(17) cm(-3), as in the regiorandom polymer. We also find that the charge carrier mobility (10(-6)-10(-7) cm(2)/Vs) does not seem to depend significantly on side-chain regularity. Photoluminescence is very similar to that in the regiorandom material, indicating efficient spectral diffusion.