This invention concerns a family of chimeric antibodies with high affinities to a high molecular weight, tumor-associated sialylated glycoprotein antigen (TAG-72) of human origin. These antibodies have (1) high affinity animal V.sub.H and V.sub.L sequences which mediate TAG-72 binding and (2) human C.sub.H and C.sub.L regions. They are thought to produce significantly fewer side-effects when administered to human patients by virtue of their human C.sub.H and C.sub.L antibody domains. The nucleotide and amino acid sequences of V.sub.H.alpha.TAG V.sub.H, CC46 V.sub.H, CC49.sub.H, CC83 V.sub.H, and CC92 V.sub.H, and CC49.sub.L, CC83 V.sub.L, and CC92 V.sub.L idiotype sequences are disclosed, as well as in vivo methods of treatment and diagnostic assay using these chimeric antibodies.