Carson McCullers' psychotherapist, friend, and physician; resident of Nyack (Rockland Co.), N.Y. Chiefly letters to Dr. Mercer from Mary Tucker, Carson McCullers' piano teacher and long-time close friend, mostly about McCullers, with a few copies of letters from Mercer to Tucker. Topics include McCullers' mental and physical health; Mercer's care of the young woman; McCullers' work, long illness, death, and funeral; Tucker and Mercer's love and admiration for the author; and their opinions on various McCullers biographers. Later letters contain mostly information about Tucker's family. An unsigned letter from Carson McCullers, dated 5 May 1962, is also in the collection.

The Mary E. Mercer Collection of Carson McCullers-Mary Tucker Correspondence, 1959-1976, contain letters written primarily to Dr. Mercer by Mary Tucker, Carson McCullers's piano teacher and a long-time close friend. Most correspondence concerns the life and work of McCullers; however, there are also several letters written after the death of the author, regarding her biographers and the allocation of her papers to various libraries. Topics include the writer's mental and physical health, her work, and Tucker and Mercer's love and admiration for the author. There is also correspondence between Tucker and Mercer regarding various biographers of McCullers and the purchase of her papers by Duke University. The papers also include several copies of Mercer's own letters and a slide of Mary Tucker taken by Mary Mercer. Arranged in chronological order.