The combination of high pressure, high magnetic fields as well as low temperatures is a wonderful tool to go into the physics of the highly correlated systems. Crystalline organic conductors constitute one class of those systems. The plan of the talk is about: i) the role of pressure in these highly correlated materials, ii) techniques of high pressure, which are common to both inorganic and organic conductors, and finally iii) the recent works on the organic conductor, HMTSF-TCNQ, studied in magnetic fields up to 31 Tesla combined with high pressure, where quantum oscillatory behavior and an unusual hysteretic behavior were seen in magnetoresistance data.