distinction may be drawn between studies that define potential mechanisms of control, those that define components of control systems, and those that determine the priority of controls in the integrated system. It is the priority controls that determine survival in the environment. These different kinds of studies are necessary and complementary. In the case of the bronchial circulation, we continue with an era of defining potential mechanisms and component systems. These have been excellently reviewed by Godden (1990) and by Coleridge & Coleridge (1994). However, we have a long way to go before we establish priority neural controls in the integrated system. Cogent examples in the bronchial circulation might be the interaction at rest between neural controls and tonic NO released from vascular endothelium in determining basal autonomic tone. Another might be the autonomic controllers of bronchial resistance vessels reflexly evoked at the onset of exercise, and how these controls are modified by central temperature regulation as exercise continues. These kinds of data are necessary to understand evolutionary mechanisms that protect the organism from untoward environmental influence, and that point to support therapies for systems breakdown.