In 1923 with the "Sieben Lieder mit Klavier" ("7 Songs with Piano") he witnessed a series of successful performances of his works, which lasted until the beginning of the 1930s ("Sieben Serenaden"). At the Geneva music festival of the International Society for New Music in 1929, his "Schönberg Variations", a piano cycle on a theme by his teacher in Vienna, caused something of a stir. Five years later, for the orchestral arrangement of this work, he was awarded the , named in honor of the former director of Universal Editions. In the meantime he had been appointed conductor in Zürich for two years. As a result of his interest in anthroposophy, a movement founded by Rudolf Steiner, he spent another two years as a bookseller in Stuttgart, but was forced to flee Germany in mid-1933 and returned to Prague as a music teacher and journalist. During this period he worked with the department of music at Czechoslovak Radio, wrote book and music reviews for various magazines, wrote as a critic for the "Bohemia" newspaper, lectured to educational groups, gave private lessons, and was actively involved in the program of the Czechoslovak Society for Music Education. At about this time Ullmann made friends with the composer Alois Hába, whom he had known for some time. Ullmann enrolled in Hába's department of quarter tone music at the Prague Conservatory, where he studied from 1935 to 1937. While his works of the 1920s still clearly show the influence of Schönberg's atonal period, especially the Chamber Symphony Op. 9, the George Songs Op. 15 and "Pierrot Lunaire", Op. 21, Ullmann's compositions from 1935 onwards, like the String Quartet No. 2 and Piano Sonata No. 1, are distinguished by a musical development that is more independent of Schönberg's inspiration. Similarly the opera "Fall of the Antichrist" develops the issues raised by Alban Berg's opera "Wozzeck". Dissonant harmonics, highly charged musical expression, and masterly control of formal structure are characteristic of Ullmann's new and henceforth unmistakable personal style. On 8 September 1942 he was deported to the Theresienstadt concentration camp. Up to his deportation his list of works had reached 41 opus numbers and contained an additional three piano sonatas, song cycles on texts by various poets, operas, and the piano concerto Op. 25, which he finished in December 1939, nine months after the entry of German troops into Prague.