Reunited with the cast in Theresienstadt, Krasa reconstructed the full score of the opera, based on memory and the partial piano score that remained in his hands, adapting it to suit the musical instruments available in the camp: flute, clarinet, guitar, accordion, piano, percussion, four violins, a cello and a double bass. A set was once again designed by Frantisek Zelenka, formerly a stage manager at the Czech National Theatre. On 23 September 1943, Brundibár premiered in Theresienstadt. The production was directed by Zelenka and choreographed by Camilla Rosenbaum, and was shown 55 times in the following year.

A special performance of Brundibár was staged in 1944 for representatives of the Red Cross who came to inspect living conditions in the camp; what the Red Cross did not know at the time was that much of what they saw during their visit was a show, and that one of the reasons the Theresienstadt camp seemed comfortable was that many of the residents had been deported to Auschwitz in order to reduce crowding during their visit.

Most of the participants in the Theresienstadt production were transported to Auschwitz and killed shortly after the performance for the Red Cross was over. One child, Ela Weissburger, who played Kocour, or the Cat, survived because she was taken ill and in the infirmary — Krása was later exterminated in Auschwitz.

One American version first performed in 2006 seeks to put the history front and center. Entitled Brundibar: Hear My Voice, this version, which was a co-production of Tucson, Arizona’s Arizona Onstage Productions and The BASIS School, uses the original Hans Krasa score and Adolf Hoffmeister dialogue. Spliced into the opera are new scenes written by Colin Killick, a high school student who had studied Brundibár. These new scenes tell the history of the piece, depicting Hans Krasa and others who worked on the piece in Terezin working on Brundibár, from the first performance of Brundibár in Prague in 1941 all the way up to the Red Cross performance in 1944. Apart from Krasa, one of the most prominent characters in these new scenes is Friedl Dicker-Brandeis, the art teacher whose students in Terezin created the heart-rending Holocaust children’s artwork that has been shown throughout the world. In the Tucson production, all of the children’s roles were played by middle and high school students (as in the original) and only the new roles were played by adult actors.

The first performances of this version were on March 31 and April 1 2006 at the Temple of Music and Art in Tucson, Arizona, under the direction of the artistic director of Arizona Onstage Productions, Kevin Johnson. In addition to the new scenes, it also featured projections of artwork from camp inmates (both children and adults) and photographs of Terezin. Ela Weissberger, the survivor from the original performances, spoke after each performance about her experiences in the cast of Brundibár and her thoughts as to its message. For this production, the new scenes were done as a staged reading (the new material is written largely in pentameter, but was read as dialogue).