A thin section of the methanogenic archaebacterium, Methanoplanus limicola, shows that the surface glycoprotein array (S-layer) is separated from plasma membrane by a distinct inter-space, approximately 4.0-6.0nm wide. We report our structural study of the S-layer by electron crystallographic techniques. Image analysis and thin sections of the S-layer treated with and without triton disclosed that retention of the single layer crystal requires the presence of detergent to avoid hydrophobic bonding.