The conjugation of antibodies with HRP by use of glutaraldehyde was proposed by S AVRAMEAS (1969). Glutaraldehye conjugation is preferably done in a “two-step” technique (AVRAMEAS S and TERNYNCK T 1971). Much earlier, glutaraldehyde was already employed for tanning in the leather industry (SELIGSBERGER L and SADLIER C 1957), and this aldehyde was introduced by DD SABATINI et al. (1963) for the fixation of biological specimens in electron microscopy. The fundamental ideas on the reaction of glutaraldehyde with proteins were given by JH BOWES and CW CATER (1965). Amino acid analyses have shown that glutaraldehyde reacts almost exclusively with ε-amino groups of proteins.