The electronic properties of aligned carbon nanotube films have been i
nvestigated by conduction electron spin resonance (CESR) and transport
measurements. Hall effect and CESR reveal that the nanotubes behave l
ike a semimetal with 10(19) carriers/cm(3) at room temperature. The in
trinsic resistivity is an order of magnitude lower than the de resisti
vity of the films. Strong deviations in the physical characteristics s
uggest a charge-carrier localisation below 40 K. Low level of doping w
ith Potassium strongly modifies the electronic properties of the nanot
ubes.