Weichselbaum is remembered for his contributions made in the field of bacteriology, and in 1887 was the first to isolate the causative agent of cerebrospinal meningitis, which he called Diplococcus intracellularis meningitidis. He is also credited with providing the first comprehensive description of local bone erosion in arthritis. Weichselbaum did important research involving tuberculosis, and founded the first Lungenheilstätte (pulmonary health institute) in Austria (Alland, Niederösterreich).