The dense plasma phase of a dynamic z-pinch working at a high filling pressure is studied. By using the Schlieren-technique it is found that the compressed plasma column, though macroscopically stable for times less than 1 μs develops quickly from a homogeneous state to a turbulent one with a perturbation scale length of typically some millimeters. Quantitative measurements of light deflection give electron densities of typically 1019 cm-3 at 0.25 Torr He filling.