CC49 is a second generation monoclonal antibody (mAb) with high affinity to a pancarcinoma antigen, TAG-72. A single-chain Fv (sFv) of CC49 may have a role in managing human carcinomas. Most reported sFvs have been expressed as insoluble products that must be solubilized and renatured. Soluble sFv expression is advantageous as activity can be assayed directly from the periplasmic fraction. Also, gene-level immunoconjugates may not be amenable to refolding protocols. Using a vector that carries the tac promoter and omp A signal, we have examined the effects of four variables on the expression and accumulation of soluble CC49 sFv: (i) linker sequence joining VL and VH, (ii) isopropylthio-beta-D-galactoside concentration for induction, (iii) temperature, and (iv) the addition of non-metabolizable sugars to the medium. We have been able to demonstrate, using rapidly prepared periplasmic extracts, that the yield of soluble sFv improves by the addition of 0.4 M sucrose to the medium and by inducing expression with a very low concentration of IPTG (0.02-0.03 mM). Under these induction conditions periplasmic extracts demonstrate increased expression of the sFv, as shown by the larger amount of a 27 kDa band on SDS-polyacrylamide gel, and an increased ability to inhibit binding of the mAb CC49 to immobilized tumor extracts.