The effect of cold on platelet adenine nucleotide (PAN) metabolism was studied. Spontaneous aggregation which occurs when chilled platelet-rich plasma (PRP) is simultaneously warmed and stirred was not accompanied by the changes in adenine nucleotides associated with the release reaction. Connective tissue caused the release of the same amount of ADP and conversion of equal amounts of ATP to IMP and hypoxanthine in cold-stored platelets as it did in room temperature stored platelets. However, cold did have an important effect on PAN. In PRP stored at cold (0° C, 3° C) temperatures and warmed up to 37° C in the presence of 3H adenine, there was an increase in the conversion of adenine to its metabolites and ultimately to hypoxanthine as compared to PRP stored at warmer temperatures. This effect could not be prevented by ouabain, prostaglandin E1, antibody to immunoglobulin M or adenosine.