Chimeric antibodies comprised of the variable region of an antibody chain contiguous with a polypeptide other than the constant region of that antibody chain are disclosed. Such chimeric antibodies can be comprised of the variable region of a chain of an immunoglobulin of selected specificity and an extrinsic polypeptide. In addition to the variable region of a chain of an immunoglobulin of selected specifity and an extrinsic polypeptide, the chimeric antibodies can include at least a portion of the constant region of an immunoglobFUNDING SOURCESThe work described herein was supported by grants from the National Institutes of Health, the American Cancer Society and the Damon Runyon--Walter Winchell Cancer Fund.