Millimeter-sized cobalt doped rutile crystals with a bi-pyramidal shape are obtained by chemical vapour transport using scroll-type H2Ti3O7 nanotubes as a precursor in which Co2+ ions are introduced by a simple ion exchange method prior to the growth. Despite the low concentration of Co2+ dopants (5 x 10(19) cm(-3)), the resistivity of the single crystal shows a metallic behaviour above 50 K and the Seebeck coefficient has the signatures of polaronic quasiparticles. The magnetic properties of the material show a weak anti-ferromagnetic interaction between the spins on Co atoms below 50 K. This synthesis method could be beneficial for the growth of a large variety of doped TiO2 single crystals. (C) 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.