In order to investigate valency, infectivity and display quality of the pJuFo phagemid, which has proven a versatile vector for the screening of cDNA libraries of various allergic sources [18], human tumor cells [19], mice B cells [27], and human fibroblasts [20], we generated pJuFo-PhoA phagemids in which PhoA was either fused to the minor coat protein pIII or to the major coat protein pVIII via a Jun-Fos linker. The gene discussed is FOS; the disease is neoplasm.