Bovine pancreatic trypsin inhibitor (BPTI) has long served as an important model system for the studies of the protein folding process. Recently a kinetically important folding intermediate has been detected early on the oxidative folding pathway of BPTI [Dadlez, M., & Kim, P. S. (1995) Nat. Struct. Biol. 2, 674-679]. The intermediate, named [14-38], contains a single native disulfide bond between residues 14 and 38, and forms much faster than any other single-disulfide intermediate. A series of 24 mutants of BPTI has been studied here to detect amino acids which contribute to fast formation of [14-38]. Seven nonpolar or aromatic residues, distant from the cysteines by as many as eight residues, are found to accelerate the formation of 14-38 disulfide, without changing the reactivities of the cysteines. The acceleration is observed even in 8 M urea. It is concluded that in the early stages of the folding of BPTI and BPTI-like domains, the residual structure of the denatured state promotes native pairing of cysteines by way of interaction of hydrophobic residues. A similar mechanism may facilitate early steps in the folding of proteins in general.