The SLC26A4 gene encodes Pendrin, an anion transporter believed to underlie I^– exit into the thyroid follicular lumen, a critical initial step in thyroid hormone production. Pendrin mutations are linked to Pendred syndrome, a human disease characterized by deafness and, occasionally, hypothyroid goiter. However, the Slc26a4^-/- mouse is systemically euthyroid, suggesting that other anion transport proteins contribute to I^– efflux ¹. One candidate is Slc26a7, an anion channel capable of conducting I^– that is found in the kidney and the stomach ^2,3. Gene microarray analysis showed strong presence of two SLC26A7-specific probes in mouse thyroid (n = 3 replicates). Subsequent mining of mouse tissue GEO database records indicated that thyroid SLC26A7 levels exceed those present in kidney and stomach. The rabbit polyclonal anti-Slc26a7 antibody, 968,⁴ recognised two bands, one migrating at ~ 85 kDa and another at ~ 65 kDa in samples of mouse total thyroid lysate (n = 3); bands at the identical position were detected in Slc26a7-injected, but not water-injected, Xenopus oocyte lysates. Because subclinical hypothyroidism has been documented for cystic fibrosis (CF) patients, we tested whether the cystic fibrosis transmembrane conductance regulator (CFTR) mediates thyroid I^– transport via effects on SLC26A7. We established a novel porcine thyroid model for CF. Thyroid glands from CFTR^+/+, ^+/- and ^-/-(wt, het, ko) piglets were shipped overnight on ice from the laboratory of Prof. M. Welsh, U.Iowa, HHMI ⁵. Glands were divided for 1) primary culture, 2) preparation of total tissue protein lysates or 3) fixation with 4% paraformaldelhyde for preparation of paraffin sections. Gross histology and transepithelial resistance did not differ significantly between wt, het and ko thyroids (wt: 2394 ± 753 Ω^.cm²; het: 2617 ± 1147 Ω^.cm²; ko: 3842 ± 1005 Ω^.cm²; mean ± sem; n = 3 monolayers; p > 0.05 between all groups; paired t-tests). A mouse monoclonal anti-Slc26a7 (14H5; Abcam) recognised the 85 kDa, but not the ~65 kDa, band in CFTR^+/+ and ^+/- pig thyroid lysates. Conversely, rabbit polyclonal antibody 968 showed the 65 kDa band, but did not detect the 85 kDa band. CFTR knockout markedly decreased the 85 kDa species (n = 3). These findings suggest a functional relationship between CFTR and SLC26A7. Future work will include measurement of I^– secretion by primary thyroid cultures derived from CFTR^+/+, ^+/- and ^-/- pigs, as well as by CFTR^-/- thyroid monolayers with knock-in of SLC26A7, or CFTR^+/+ with knock-down of SLC26A7. Possible functional coupling of CFTR and SLC26A7 via PDZ-domain interactions also will be explored.