The aim of this research was to investigate whether cyclosporin‐A (Cy‐A) could exert its action on graft rejection in progress. For this purpose, heartlung grafting was performed in a strong hystoincompatible combination of rats (BN/LEW). In one group of animals, Cy‐A was administered at the dose of 15 mg/kg daily for 10 days starting on the 5th day after grafting. In a control group only olive oil was administered. Five of six animals treated with Cy‐A showed a graft survival over 4 weeks and in two cases it was over 2 months when they were killed.