Diagnostic occlusion is used in strabismus to examine the changes in the angle of squint after a period of disrupted fusion. The aim of the present study was to investigate the effect of diagnostic occlusion on ocular alignment in normal subjects without strabismus and other ocular motility related symptoms. Diagnostic occlusion of the non-dominant eye was applied to ten subjects for three days. In all cases a small horizontal deviation was seen in the primary position and in three cases also a small vertical deviation was noted. Diagnostic occlusion for seven days was applied in nine persons. Changes in alignment of approximately the same size as after three days of occlusion were seen. In both groups incomitances of ocular alignment were noted that indicate small muscle imbalances particularly in the oblique muscles of normal subjects that are easily compensated by normal motor fusion.