Abstract: This invention concerns a subset of composite Hum4 V.sub.L, V.sub.H antibodies with high affinities to a high molecular weight, tumor-associated sialylated glycoprotein antigen (TAG-72) of human origin. These antibodies have variable regions with (1) V.sub.L segments derived from the human subgroup IV germline gene, and (2) a V.sub.H segment which is capable of combining with the V.sub.L to form a three dimensional structure having the ability to bind TAG-72. In vivo methods of treatment and diagnostic assay using these composite antibodies is also disclosed.