Magnetoconductance of carbon nanotubes (CNTs) is investigated. We clearly show that a semiconducting CNT can be converted into a metallic one, or vice versa, with the application of a large magnetic field parallel to the tube axis, providing a consistent confirmation of the Aharonov-Bohm (AB) effect on the band structure of CNTs. Wealso demonstrate that magnetic-field values where the semiconductor-to-metal transition occurs can be tuned by mechanical strain. Combined control of both the strain and the AB effect may open up new possibilities for CNT devices. In addition, we propose an idea to manipulate spin-split subbands of CNTs, resulting from spin-orbit interaction (SOI), by using the magnetic field to generate sizeable spin-polarized currents. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim