We studied by scanning electron microscopy the effects of the repeated use of a newly-designed, disposable, suction trephine (Microsurgical, Ltd, Bedfordshire, England) on the nature of the cut of successive corneal buttons from sheep eyes. After the trephine was used more than nine times, the cut edge became more irregular as successive buttons were produced. Also, progressively greater degrees of endothelial cells adjacent to the cut edge were lost. Although the corneal buttons initially were circular, those produced after the 20th cut became more oval. These results suggest that a disposable corneal trephine should be reused no more than nine times.