A crude extract of axenically grown amoebae was used as antigen in order to develop an AB microELISA for the detection and quantitation of E. histolytica-specific IgG antibodies. This ELISA was used to screen individual sera of patients suffering from invasive amoebiasis (n=47)and control individuals(n=33). Significant titers of E-histolytica- specific IgG antibodies were present only in sera of patients suffering from invasive amoebiasis. The AB-microELISA had a sensitivity of 98% and a specificity of 97%. Immunoblot analysis of the crude E. histolytica extract indicated the presence of several antigenic proteins. One of the common antigenic proteins recognized by the individual patients' sera had a molecular weight of 160.170 kDa Sera of five patienta with high titers of E. histotytica-specific IgG antibodies were used to prepare a serum pool. This pooled serum was used for immunoscreening of an E. histolyitca cDNA expression library prepared in the phage vector l ZAP-II. A strongly immunoreactive phage done was identified, from which he recombinant phagemid was released by in vivo excision for characterization of the cDNA insert.