With rabbit corneas we did comparative biomicroscopical and histological investigations on material tolerance of the following threads at present used in microsurgery: Barraquer silk (virgin silk), nylon 30 mum (Tübinger nylon), dacron (polyester) 40 mum and plain collagen 7-0. The sutures were implanted into the cornea intra-lamellarly, completely under the microscope. The examinations showed only very little tissue reaction in all these materials.