We have studied the development of instabilities, primarilym = 0modes, in CD2fiber z pinches. Two simultaneous optical diagnostics have been used in order to obtain an unambiguous picture of the dynamics. The first is two‐dimensional interferometer using a short‐pulse laser. The second is multi‐frame two‐dimensional schlieren/shadowgraphy camera. The interferometer serves as a check on the schlieren/shadowgraphy camera helping to overcome uncertainties in interpretation of the schlieren/shadowgraphy results. An x‐ray polychromator is used to measure electron temperature. Growth of the unstable modes is compared with predicted growth rates. There are indications that some forms of current prepulse can have a significant effect on the long‐term development of instabilities.