Among the many musical activites in Terezín choral singing was one of the most popular. Klein's fellow inmates provided the resource for his beautiful settings to well-known Russian and Slovak folk tunes.

Chamber Music was one of the most preferred genres of the so-called Terezín composers Hans Krása and Gideon Klein. Their oeuvres for strings includes duos, trios and quartets orginating from pre-war times as well as from Terezín.