The emergence of turbidity in startup flows of aqueous solutions of cetyltrimethylammonium bromide (CTAB)/sodium salicylate (NaSal) between parallel discs was investigated. An induction time and a critical shear rate required for the emergence of turbidity were measured for solutions of several molar concentration ratios of NaSal to CTAB and at several temperatures. The critical shear rate depends on the relaxation time of CTAB/NaSal solutions. Furthermore, the dependency was classified according to the concentration ratio into three groups. These results indicate that the emergence of turbidity depends on the network structure of wormlike micelles that varies with the concentration of counter ions. In addition, it was found that a critical Weissenberg number defined by the product of the relaxation time and the critical shear rate was constant for each group. (C) 2012 The Society of Rheology. [DOI: 10.1122/1.3676001]