In situ Laue analysis during microcompression is carried out on Mo-alloy pillars containing defects due to focused ion beam milling or pre-strain. Independently of how the defects are introduced, if the diffraction peaks are streaked prior to deformation, slip starts in the direction matching the observed streaking, even if this corresponds to a low Schmid factor. The amount of pre-strain influences the deformation behaviour in terms of hardening and strain bursts.