To determine whether exposure to the excimer laser beam results in the oncogenic transformation of cornea cells, tissue-cultured corneal keratocytes and intact corneas from an inbred strain of rat were exposed to ablative and subablative energies of the excimer laser beam. No evidence for cellular transformation was found. Neither the corneas nor the stromal keratocytes exposed to the laser beam were transformed into cells with unregulated growth potential. Both treated keratocytes and corneas were implanted subcutaneously in the same strain of rats; neither developed into tumors. In tissue culture, cells from cultures exposed to the excimer laser beam exhibited normal growth patterns, growing at the same rate as control, unexposed cells and exhibiting the same capacity to respond to the contact inhibition of growth as the control cells. These results suggest that the 193-nm excimer laser beam does not transform corneal keratocytes and that the energies emitted by this beam will not cause cell transformation when the excimer laser is used as a surgical tool in human eyes.