The purification and characterization of polyclonal and monoclonal antibodies and antibody-enzyme conjugates by high-performance liquid chromatography (HPLC) using a Protein Pak 300 SW column and a Protein Pak DEAE anion-exchange column is described. The following polyclonal antibodies were examined: (i) donkey anti-mouse immunoglobulin G (IgG), (ii) mouse IgG, (iii) sheep anti-human IgG and (IV) goat anti-human factor VIII. HPLC was used to analyse the purity of horseradish peroxidase conjugates of rabbit anti-mouse IgG and donkey anti-mouse IgG. In the case of donkey anti-mouse IgG, each stage of the production of the purified antibody and antibody-enzyme conjugate was monitored by HPLC. HPLC was used to examine monoclonal mouse anti-human T cell and mouse anti-human apoliproprotein B antibodies. The presence of antibody in ascites fluid from mice bearing Landschütz ascites tumour cells was also detected. The antigen-antibody reaction between human serum albumin and anti-human serum albumin was demonstrated using HPLC and this procedure should offer a novel method for studying antigen-antibody interaction.