Abstract: A peptide according to the present invention is not more than 40 amino acids long and contains a sequence which is at least 6 amino acids long from the amino acid partial sequence between the amino acids 144 and 183 of human .alpha.1-microglobulin or/and a sequence which is at least 6 amino acids long from the amino acid partial sequence between the amino acids 1 and 20 of human .alpha.1-microglobulin.An antibody according to the present invention is capable of specific binding to a peptide according to the present invention as well as to human .alpha.1-microglobulin.In order to determine human .alpha.1-microglobulin in a sample liquid by an immunoassay, the sample liquid is brought into contact simultaneously or sequentially with defined amounts of the components antibody and peptide whereby one of the components is labelled and the determination is carried out by means of this label.