The aim of the talk is to discuss the electronic transport properties of metallic single walled nanotubes in the presence of defects. Two different types of defects will be considered: the first one is a strong localized defect produced by squashing the nanotube with the tip of an atomic force microscope. The radial deformation so induced produces a gap opening that decrease the low voltage conductance up to one order of magnitude. The second types of defects are weak defects uniformly distributed along the length of the nanotube. Consecutive ion irradiation doses are applied to nanotubes producing the uniform density of defects. After each dose the electrical characteristics of the same carbon nanotube are measured by using a conductive atomic force microscopy. Theoretical simulations demonstrate that only di-vacancies are relevant to explain the conductance drop induced by the irradiation. The data show that only a 0.1% of defects cause the resistance of a 400 nm length nanotube to increase three orders of magnitude.