Radiation exposure is known to impair healing in irradiated areas. Fibroblasts play a major role in the production and modification of extracellular matrix in wound repair. Since one important aspect of wound repair is the contraction of the wound, this study investigated the effects of radiation on the ability of fibroblasts to mediate collagen gel contraction in an in vitro model of wound retraction. After irradiation, the cells were detached and suspended in a solution of rat tail tendon collagen. Radiation exposure decreased retraction, and this effect was dose dependent. In order to define the mechanism of reduced gel retraction, we investigated alpha2beta1 cell surface integrin and fibronectin, which are thought to mediate contraction, and prostaglandin E2 (PGE2), which is known to inhibit this process. PGE2 release increased dose responsively following radiation. The cyclooxygenase inhibitor indomethacin could partially restore the contractile activity of irradiated fibroblasts. Fibronectin production in gel culture showed a significant decrease. In contrast, there was no decrease in alpha2beta1 integrin expression in radiated cells. In conclusion, radiation decreases fibroblast-mediated gel contraction. Increased PGE2 production and decreased fibronectin production by irradiated fibroblasts may contribute to this effect and may be in part responsible for poor healing of radiated tissue.