Holzmaden "Laggerstatten" is famous for its complete vertebrate skeletons. Geochemical and biochemical analyses were performed on ichthyosaur bones (Stenopterygius) and surrounding sediment to investigate the state of preservation of mineral and organic fractions. SEM observations and electron microprobe analyses show that fossil bones s. s. are slightly altered. The organic fraction is rather poorly preserved. Infrared analyses indicate that the main bands characteristic of the organic matrix are absent or altered in fossil bones. Amino acid analyses do not reveal amino acids that could be attributable to the original organic matrix. In gel electrophoresis, both sediment and bone soluble extracts showed the same pattern with only faint bands. Tentative identifications of components with immunological assays using bovine collagen and osteocalcin antibodies failed to reveal unambiguously these proteins. These results are discussed in relation to causal agents of fossilization occurring in the Holzmaden site.