In 1929 Mandyczewski died, and it may have been this, together with the successes that his compositions had enjoyed in Germany, that led Gál to apply for the vacant position of Director of the Conservatory in Mainz, in the Rheinland. As he put it in his letter of application, 'my works have been published by German publishers and been performed in nearly all German cities; I think, therefore, with respect to all my activities so far, that I would not be considered a foreigner in Germany.' He was one of 120 applicants for this post, but he had strong support from his referees, among them Wilhelm Furtwängler, then conductor of the Berlin Philharmonic Orchestra, Fritz Busch, conductor and director of the Dresden opera, and the directors of the opera houses in Breslau and Frankfurt. It is also possible that Richard Strauss added his influence on Gál's behalf. After a rigorous selection procedure, Gál was appointed to the post, which he took up on 3rd December, 1929, by a unanimous decision of the appointing committee, endorsed by the city fathers. His family followed him there in March, 1930, taking up residence in a splendid art-nouveau house with a large 'ox-eye' window overlooking the Rhein:

"The view of the Rhein and the lively traffic there I always found wonderful. We had a window overlooking the Rhein, it was round in art-nouveau style and was so to speak an ugly landmark in Mainz. But looking out of this round window was wonderful."

The post was certainly no sinecure; the conservatory had about 1000 students and 70 teachers, and Gál was fully involved in its activities. He himself directed the choirs and orchestra, as well as taking the conducting class and the courses on counterpoint, harmony and composition, and he still had a few piano pupils. He set out his goals for the conservatory in an article in the local press, which appeared only a few weeks after his appointment:

"Even those who are already predisposed to music must, so to speak, be awakened to a higher, more intensive, truly artistic musical sensitivity, as musicians as well as listeners . . . This capacity for productive listening and experiencing, which I should like to call artistic receptivity, is, as any attentive observer can confirm, in serious decline today, in spite of all attempts to spread culture more widely. The main deficiency in this respect is, in brief, in the teacher's ability to bring the musical work of art to life for the student to whom he is supposed to be conveying it . . . Real enthusiasm, true joy in music comes only from a masterpiece, never from something worthless or insignificant, which cannot satisfy anyone in the long run. Therefore bad music is much, much more damaging than is generally assumed, it destroys not merely tase but also indirectly the pleasures of music . . . Artistic sensitivity and musical enthusiasm can . . . only be learnt from the masterpieces of the great composers; and the best way to achieve it is naturally through practical music-making." [ Mainzer Anzeiger, 31.12.1929 ]

In pursuit of these goals Gál appointed a number of distinguished musicians to the staff of the conservatory, among them the Viennese pianist Louise Wandel. He also founded a women's choir and madrigal ensemble - he was jokingly referred to as 'Hans Madri-Gál'.

A vivid portrait of Gál's own teaching is presented by Otto Schmidtgen, a student at the time - and much later a successor as director of the conservatory and a committed promoter of his music:

"Gál's teaching was extremely instructive, supported by comprehensive knowledge and an extraordinary familiarity with the literature, which still amazes me today. Teaching from such a lofty standpoint can hardly be fitted into a 'timetable' . . . It was never the case that only the work under discussion was mentioned, the horizon was very broad, so that for example in talking about the 'Rosenkavalier' problems were suddenly discussed which related to Bach and Mozart. The teaching had nothing schoolmasterly about it, but had rather the character of a friendly talk . . . We all sensed that he was a personality of a quite special stamp who stood head and shoulders above everyone else." [Waldstein, op. cit., pp. 91-2.]

One thing that Gál did not do was to allow his students to study any of his own works, and none of them were ever performed at the conservatory. They were naturally performed, however, to appreciative audiences, in concerts in the city itself.

According to Hanna Gál, the intense activity of the job offered Gál a way of dealing with the loss of his friend and mentor Mandyczewski. As she put it,

"The stimulating and very tiring work in Mainz helped him over the loss. In Vienna it would have have been dreadful! No Mandy in the archive of the Gesellschaft der Musikfreunde, no Mandy in the director's box in the auditorium at the Musikverein, no Mandy, who knew more than the best encyclopaedia, no Mandy, the good friend and adviser!" [Private correspondence, October, 1989.]