Hyluronic acid (HA) on tissue healing has been controversial. We examined the molecular pharmacology of HAinjection at the suture site in an acute model of supracoracoid tendon laceration using chickens, an injury of a nonweight-bearing joint considered similar to the human shoulder. Expression of mRNAs encoding α I (I) and αI (III) procollagens was localized using in situ hybridization (ISH). Intensities of m RN Aexpression for α I (I) and α I (III) procollagens, transforming growth factor-β1 (TGF- β1), basic fibroblast growth factor (bFGF), and insulin-like growth factor (IGF) were determined by quantitative reverse transcription-polymerase chain reaction (RT-PCR). Histologically, chickens with HA injection (HA group) showed early restoration of continuity at the laceration site than saline-injection controls (saline-injection group). By ISH, the expression rate of cells at the lesion site that contained α I (I) and α I (III) procollagen mRNAswere somewhat higher in the HA group than in the saline-injection group. By RT-PCR, the HA- and saline-injection groups showed no significant difference in expression of α I (I) and α I (III) procollagen mRN A bet ween weeks 1 and 6. The saline -injection group exhibited significant decrease in TGF-β1 expression between weeks 1 and 3, and in bFGF expression between weeks 1 and 2; however, the HA group showed no such decrease. As for IGF, no difference was appreciable in both groups between weeks 1 and 6. A single injection of HA could cause earlier restoration of continuity at the lacerated site of the supracoracoid tendon. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:173–184, 2007