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The first measurements of AVT-sensitive adenylate cyclase activity in specific segments of the nephron of the Australian arid-zone agamid lizard, Ctenophorus (=Amphibolurus) ornatus, are reported. All sections of the collecting-duct system of this lizard were found to be sensitive to AVT at a concentration of 1 X 10(-6) M. In addition, receptors to AVT were located in the thin-intermediate segment linking proximal and distal convoluted tubules. No significant response to AVT was detected in the glomeruli, in either proximal or distal convoluted tubules, or in the ureter. The physiological significance of these particular segments is discussed in terms of the action of AVT in stimulating water and salt reabsorption in the lizard kidney. (C) 1996 Academic Press, Inc.