Previous work has shown that ATP and adenosine 3'-5'-monophosphate (CAMP) levels in various tissues decrease during shock and that treatment of animals in shock with ATP-MgCl2 restores the tissue ATP levels. Since the formation of CAMP is through ATP, CAMP levels might also be restored by ATP-MgCl2 treatment. Fasted Holtzman rats were bled to a pressure of 40 mmHg and maintained for 2 hrs. ATP-MgCl2 (0.25 ml 25 μmoles each) or saline (0.25 ml) was then infused i.v. and followed by the return of the remaining shed blood. 20 minutes after the above treatment, animals were sacrificed and liver, kidney, muscle and brain were quickly removed and frozen in liquid N2. CAMP was measured by radioimmunoassay. The levels of CAMP (picomoles/gm; mean ± SEM; n = 8 for each value) in liver, kidney, muscle and brain were: 1242 ± 88, 1602 ± 97, 917 ± 70 and 3785 ± 470, respectively. During shock, CAMP levels in the above tissues decreased to 482 ± 36, 627 ± 48, 676 ± 57 and 2289 ± 264, respectively, and these values did not change following saline-blood infusion. CAMP levels of animals treated with ATP-MgCl2 and blood following shock increased to 1195 ± 90, 1710 ± 100, 1186 ± 84 and 4062 ± 490, respectively. The precise mechanism for the restoration of CAMP levels following shock by ATP-MgCl2 treatment is not known at present.