In a total of eight experimental groups, PGS, PGS-S, PGS-C, and polyglactin 910 sutures were implanted subcutaneously in rats. The sutures were either sterile or contaminated with staphylococcus. They were removed after 7, 14, 21, and in two groups after 28 days. The linear loss of tensile strength was tested by means of an electronic tensile strength measuring machine. In four additional groups, the same studies were carried out with paraffinized PGS sutures and in localizations in stomach, duodenum and colon. The diameter of the filament has an effect on the loss of tensile strength: initially more rapid in fine filaments and later, retarded in comparison to thicker filaments. Coating of the suture has almost no influence on tensile strength, although contaminated sutures show a comparative decrease. In intraenteral localizations, loss of tensile strength can be expected to occur much more rapidly than in subcutaneous ones. Paraffinization does not delay decrease in tensile strength. Polyglactin 910 sutures of the second generation employed subcutaneously, show a much higher loss of tensile strength on the day 7 than PGS sutures; by day 28 the relationship is reversed.