Reiss was a member of the 1956 Swiss Everest-Lhotse expedition. At the end of April and start of May, the expedition erected some high camps. From the last high camp at the Geneva Spur on 18 May, Luchsinger and Reiss climbed the summit of Lhotse mountain. Their colleagues and were successful on 23 May and one day later Dölf Reist and made the second and third climb on Mount Everest.