A synthetic peptide endowed with immunological activity is disclosed, which is capable of inducing in mammals the formation of anti-peptide antibodies capable of recognizing human alpha-fetoprotein and of reacting with it, and incapable of recognizing albumin or its degradation products, with said peptide being essentially constituted by the aminoacidic sequence of formula (I), corresponding to 38-119 region of human alpha-fetoprotein. Furthermore, the methods and means for preparing said peptide by means of the recombinant DNA techniques are reported. The synthetic peptide (I), like the polyclonal and monoclonal antipeptide antibodies are particularly suitable for the early diagnosis of hepatocellular carcinoma and of teratocarcinoma.