This series began in 1997 with the ST2 in Europe before Ducati shipped the model to the United States in 1998. Ducati added the ST4 model in 1999. The ST was partially a replacement for the Paso, but also represented a more serious entry by Ducati into the burgeoning Sport Touring market. The difference between the ST2 and the ST4 was primarily their engines, with the ST2 having a 944 cc Desmodue two-valve motor, and the ST4 using the four-valve Desmoquattro motor derived from the previous series 916 superbike. Other differences were in the construction of the frame and electrical systems, and also the choice of suspension component manufacturers.
In 2006, the ST4s production was discontinued in favor of an ST3s variant, inheriting the suspension components of the ST4s but keeping the Desmotre motor unchanged from the normal ST3. The reasons given for the ST4s’ demise are that the ST3 motor required less maintenance and would also meet Euro-3 emissions levels, where the 996 motor (in its then-current design) would not pass the more stringent emissions standard, and also required more expensive maintenance.