The Reynolds number for transition from singly to doubly periodic Taylor–Couette flow is studied experimentally and found to vary inversely with the aspect ratio &Ggr; of the fluid column. This transition Reynolds number is also dependent on the numbermof azimuthal waves. For a givenm, the type of modulating state, which results after this transition, is not affected by &Ggr;, nor does the transition Reynolds number differ for the different types of modulating states which can occur.