Lionello Lenaz was the head doctor of the Rijeka Hospital and visiting assistant professor at the University of Padua. He attended Medical School in Vienna and in 1895 received a degree in general practice.
Lenaz spent next six years working an assistant at the neurology clinics of renowned professor Benedict and professor Neusser. In 1901 he returned to Rijeka and accepted the position of director of the Bacteriological Laboratory of the city hospital.
As a professional, he is particularly remembered for his study of jaundice and kidney disease. His most extensive works "Lezioni di ematologia" (published by Wassermann), and "Lezioni di neurologia" remained unfinished. In addition, he wrote a large number of scientific papers from various medical fields (neurology, physiopathology, infectology, etc.). Lenaz was an active member of the Autonomous Party.