Herter initially practiced mainly neurological medicine in New York City. His experience was captured in "The Diagnosis of Diseases of the Nervous System", a manual he wrote for "students and practitioners" in 1892. Herter's interest in laboratory medicine led him to relinquish his medical practice and build a laboratory in the fourth floor of his house on 819 Madison Avenue. In 1897, he was appointed professor of Pathological Chemistry at University and Bellevue Hospital Medical College. His lectures were published in 1902.