The presence of large scale structures in circular jets is well documented in the literature over a wide range of Reynolds numbers. This presentation explores in more detail the generation and interaction and the role they play in the development of the flow field. It is based on experiments carried out, both in water and air jets, at Reynolds numbers up to 100 000.1,2It is found, as reported by others, that the frequency of generation, as well as the various modes of the large scale vortices, can be predicted by linear stability theory. However, their further development as they are convected downstream is most difficult to study in detail. Conventional correlation measurements or sampling techniques have proven to be inadequate. In fact, the purpose for doing parallel water and jet experiments is to enable one to develop an adequate experimental method that could provide better information on the interaction process between adjacent structures. In a qualitative way, the measurements so far suggest that the induced flow field of the structures must play an important role in the interaction process and in the flow development. In the region of the potential core there is apparently an upstream influence due to the induced pressure field. This affects and, perhaps, controls such flow characteristics as the length of the potential core and the passage frequency of the structures at the end of the core. By introducing artificial disturbances into the flow further work is being carried out to clarify the above conjecture. This research was supported by the National Aeronautics and Space Administration under Grant NASA‐NSG‐1221.