The synthesis and CRF receptor binding affinities of several new series of N-aryltriazolo- and -imidazopyrimidines and -pyridines are described. These cyclized systems were prepared from appropriately substituted diaminopyrimidines or -pyridines by nitrous acid, orthoester, or acyl halide treatment. Variations of amino (ether) pendants and aromatic substituents have defined the structure-activity relationships of these series and resulted in the identification of a variety of high-affinity agents (Ki's < 10 nM). On the basis of this property and lipophilicity differences, six of these compounds (4d,i,n,x, 8k, 9a) were initially chosen for rat pharmacokinetic (PK) studies. Good oral bioavailability, high plasma levels, and duration of four of these compounds (4d,i,n,x) prompted further PK studies in the dog following both iv and oral routes of administration. Results from this work indicated 4i,x had properties we believe necessary for a potential therapeutic agent, and 4i1 has been selected for further pharmacological studies that will be reported in due course.