- 
OJ 9/3, [1] Handwritten letter from Guido Adler to Schenker, dated October 25, 1901
 The Vienna chapter of the International Music Society invites Schenker to give
        a lecture. 
- 
OJ 9/3, [2] Handwritten letter from Guido Adler to Schenker, dated July 2, 1902
 Adler inquires whether Schenker is willing give his lecture for the [Vienna
        chapter of the] International Music Society in the coming season. 
- 
OJ 9/3, [3] Handwritten letter from Guido Adler to Schenker, dated October 5, 1902
 Adler inquires whether Schenker is willing give a further lecture for the
        [Vienna chapter of the] International Music Society in the coming season. 
- 
UG 32/5, [1] Handwritten letter from Schenker to Guido Adler, dated April 21, 1914
 Letter of recommendation for Hans Weisse 
- 
OJ 9/3, [4] Typewritten letter from Guido Adler to Schenker, dated February 10, 1926
 Invitation to join the Conference Committee of the Beethoven Centennial
        Celebration 1927. 
- 
OJ 9/3, [5] Typewritten letter from Adler to Schenker, dated January 28, 1927
 Invitation to give a lecture to the conference associated with the Beethoven
        Centennial Celebration [March 1927]. 
- 
OJ 5/3, [1] Handwritten draft letter from Schenker to Adler, dated February 7, 1927
 Schenker declines invitation to give lecture. 
- 
OJ 9/3, [6] Typewritten letter from Guido Adler to Schenker, dated April 4, 1927
 Schenker is asked to have his photograph taken as a collaborator in the
        Beethoven Centennial Celebration. 
- 
OJ 11/1, [1] Typewritten letter from Atelier Pietzner-Fayer to Schenker, dated May 10,
        1927
 Pietzner-Fayer extends the deadline for portrait photography to May
        20. 
- 
UG 32/5, [2] Handwritten letter from Schenker to Guido Adler, dated May 31, 1933
 Schenker thanks Adler for the offprint of his Brahms article.