The present invention relates to a pharmaceutical composition comprising a bispecific single chain antibody construct, said bispecific single chain antibody construct comprising binding domains specific for human CD3 and human CD19, wherein the corresponding variable heavy chain regions (V.sub.H) and the corresponding variable light chain regions (V.sub.L) regions are arranged, from N-terminus to C-terminus, in the order, V.sub.H(CD19)-V.sub.L(CD19)-V.sub.H(CD3)-V.sub.L(CD3), V.sub.H(CD3)-V.sub.L-(CD3)-V.sub.H(CD19)-V.sub.L(CD19) or V.sub.H(CD3)-V.sub.L(CD3)-V.sub.L(CD19)-V.sub.H(CD19). Furthermore, processes for the production of said pharmaceutical compositions as well as medical/pharmaceutical uses for the specific bispecific single chain antibody molecules bearing specificities for the human CD3 antigen and the human CD19 antigen are disclosed.