Abstract: A process for preparing an immunogenic conjugate of a nitroaromatic compound and a carrier comprises colavently bonding the nitroaromatic compound to the carrier in an essentially oxygen-free atmosphere and isolating the conjugate from the reaction mixture. The conjugate may be used to raise antibodies specific to the nitroaromatic hapten. The antibodies may be used to determine the presence of hypoxic tissue in living matter by treating the living matter with a nitroaromatic compound and subsequently testing suspected tissue to determine if there is binding of the antibody to tissue. By use of appropriate markers, bound antibodies can be determined to indicate the presence of hypoxic tissue due to the unique reaction of nitroaromatic compounds with hypoxic tissue.