Poly(A)+ RNA isolated from rat jejunum was injected into Xenopus laevis oocytes and expression of Cl-/HCO3- antiport was investigated by means of 36Cl- uptake. Two days after injection of 50 ng of poly(A)+ RNA, Cl- uptake was significantly increased with respect to water-injected oocytes. The expressed transport was inhibited by 0.2 mM DIDS, whereas endogenous Cl- uptake was unaffected by this disulphonic stilbene. After sucrose density gradient fractionation, the highest expression of DIDS-sensitive Cl- uptake was detected with mRNA size fraction of about 2-4 kb in length. The expressed Cl- uptake can occur against a Cl- concentration gradient and is unaffected by the known Cl- channel blocker anthracene-9-carboxylic acid. Cl- transport mechanism has properties similar to jejunal basolateral. Cl-/HCO3- exchange with regard to Na+ dependence.