Observers have offered prescriptions for IS planning in a turbulent business environment. The action research described here examined actual IS planning practices in two real-world organizations in such an environment. One organization adhered closely to many of the planning prescriptions and the other did not. Their experiences support the view that the analysis of the external environment and a continuous planning process are essential in such an environment. More importantly, they suggest that, in a turbulent environment, comprehensive IS planning (i.e., adherence to many prescriptions) is more effective than less rigorous planning. Such a conclusion may seem counterintuitive. Although the experiences facilitate the development of new prescriptions, they impugn some of the others.