The present invention relates to a binding molecule comprising at least three domains comprised in at least one polypeptide chain, wherein the first binding domain is a binding domain which is capable of binding to a cell surface molecule on a target cell, the second binding domain is a binding domain which is capable of binding to the T cell CD3 receptor complex, and the third domain is a binding domain which is capable of binding to serum albumin, wherein said third domain is positioned at the C-terminus of said second domain. Moreover, the invention provides a nucleic acid sequence encoding the binding molecule, a vector comprising said nucleic acid sequence and a host cell transformed or transfected with said vector. Furthermore, the invention provides a process for the production of the binding molecule of the invention, a medical use of said binding molecule and a kit comprising said binding molecule.