To clarify the mechanisms by which substance P (SP) and insulin-like growth factor-1 (IGF-1) synergistically facilitate corneal epithelial wound healing, we tested the hypothesis that the combination promotes cell attachment to a fibronectin matrix through up-regulation of expression of integrin alpha 5 beta 1, the major cell surface fibronectin receptor in rabbit corneal epithelial cells. Cultured rabbit corneal epithelial cells were treated with SP and/or IGF-1 and then plated on wells coated with fibronectin and bovine serum albumin. After incubation, the number of cells attached to the wells was counted. In a second experiment, reverse transcription-polymerase chain reaction was used to determine the expression of integrin alpha 5 and beta 1 by cells pretreated with SP and/or IGF-1. The combination of SP and IGF-1 significantly increased the number of cells attached to the fibronectin matrix and the expression of integrin alpha 5. However, attachment to the fibronectin matrix was inhibited by the addition of GRGDSP, a synthetic peptide that mimics fibronectin. Thus, the synergistic enhancing effect of SP and IGF-1 on the attachment of corneal epithelial cells to the fibronectin matrix and on corneal epithelial migration is partly due to the up-regulation of integrin alpha 5 expression in corneal epithelial cells.