This paper reviews solute and water transport by the organs of the avian lower intestine (coprodeum, colon and ceca). In particular, the questions of what physiological roles these transport processes play and what factors regulate them are discussed. There seems to be clear evidence that the lower intestine subserves both osmoregulatory and nutritional roles, but these functions may only be significant under conditions that stress these systems, such as dehydration, salt depletion or low protein intake. Of particular interest are studies showing physiological adjustments of lower intestinal transport properties to dehydration and salt depletion. Included in these adjustments are changes in osmotic water permeability, solute-linked water flux, apical surface area amplification and, possibly, changes in the rate of retrograde movement of ureteral urine. During salt depletion, high aldosterone levels both increase electrogenic Na + channel activity and suppress Na + -linked nutrient cotransporters. The reappearance of these cotransporters with resalination may occur by a default mechanism, or may be regulated by other hormonal or non-hormonal factors. Protein, amino acids and hexoses from both ureteral urine and proximal intestine may be recovered or recycled by lower intestinal transport. There is also evidence for urate degradation and nitrogen recycling via ammonia or amino acid transport. When acclimated to high fiber diets, there appears to be significant fermentative degradation of indigestible plant materials, that may directly or indirectly supply substrate for nutrient transporters. Finally, studies with a variety of species have demonstrated several different adaptive strategies for use of the lower intestine in post-renal modification of urine.