This article characterizes the occurrence of biphasic dose responses by adenosine and its stable analogs in numerous systems, including the respiratory tract, kidney, cardiovascular system, and brain. Considerable mechanistic research on various systems explored and clarified the interactions of the A-1 and A-2 receptors and their interactive influence on the occurrence of the biphasic dose responses. In general, the maximum stimulatory response was 2.5-fold or less than controls, while the stimulatory concentration range was quite variable ranging from 10- to 10⁵-fold.