Analysis of free nucleotide composition of both avian thrombocytes and pig platelets showed quantitative differences in the level of adenine nucleotides. 3H-adenine taken up by turkey thrombocytes was metabolized mainly to adenine nucleotides was not released after thrombin action. Thrombin liberated non-radioactive adenine nucleotides (18.2 +/- 1.5%, 20.6 +/- 1.9%) of the total, probably localized in a storage pool. Malonyldialdehyhyde (MDA) production due to thrombin was observed in both platelets and thrombocytes.