The present invention relates to novel antibodies reactive with human carcinoma cells. More particularly, the antibodies of the invention include: a murine monoclonal antibody, BR96; a human/murine chimeric antibody, ChiBR96; and a F(ab')2 fragment of BR96. These antibodies are reactive with a cell membrane antigen on the surface of human carcinomas. The antibodies display a high degree of selectivity for carcinoma cells and possess the ability to mediate ADCC and CDC activity. In addition, the antibodies of the invention internalize within the carcinoma cells to which they bind and are therefore particularly useful for therapeutic applications, for example, as the antibody component of antibody-drug or antibody-toxin conjugates. The antibodies also have a unique feature in that they are cytotoxic when used in the unmodified form, at specified concentrations.