The contrast of dislocations in icosahedral Al62Cu25·5Fe12·5was investigated in the transmission electron microscope. It was found that the contrast vanishes under two basically different diffraction conditions. This is different from the behaviour in normal crystals and is due to the special structural features of dislocations in quasiperiodic lattices. Quantitative evaluation of the results indicates that the phason component of the dislocation strain field is substantially stronger than the phonon component.