L-arginine phosphate monohydrate (LAP) organic crystals were investigated b
y X-ray Lang topography. Selected topographs of nearly perfect seeded grown
and self-nucleated crystals show that typical defects inside are grown-in
and post-growth dislocations, growth sector boundaries, and microbes, while
their features are presented and discussed. No structural defects associat
ed to the presence of step bunching on the (100) surface of the crystal hav
e been observed by X-ray topography.