Upshoot-in-adduction and downshoot-in-adduction are non-paretic motility disorders that usually accompany a horizontal squint in children, together with V- or A-pattern motility. Upshoot-in-adduction may sometime mimic a superior oblique palsy. The authors have found that even in healthy volunteers these motility disorders can be found and made manifest by patching. One eye of complaint-free volunteers with full stereopsis was patched for three days. Then the eye movements of the patched eye were recorded with the search coil technique, first before taking the patch off and secondly after putting the patch on the other eye. The latter registration served as reference for the first registration. It was found that 11 out of 18 volunteers had developed an upshoot-in-adduction of the patched eye. In five cases no directional change was found whereas two cases had developed a downshoot-in-adduction. It seems that up- and downshoot-in-adduction are latent motility disorders that become manifest after disruption of fusion. In addition, the authors found undershooting saccades and postsaccadic drift of the patched eyes.