We previously reported the identification of eight Sz. pombe cDNA clones that are capable of suppressing the heat-shock sensitive phenotype associated with deletion of IRA1 in S. cerevisiae. We report that one of these cDNA clones, pPSI5, encodes a protein, Pde1, that is 24% identical to the S. cerevisiae low-affinity cAMP phosphodiesterase. The pde1/cgs2 gene encoding this protein has been previously identified, and studies have shown that deletion of this gene results in elevated levels of intracellular cAMP and inhibition of meiosis. To demonstrate that Pde1 is a cAMP phosphodiesterase we expressed it in an S. cerevisiae strain which lacks the genomic cAMP phosphodiesterase genes. Extracts from such cells that express the Sz. pombe Pde1 exhibit high levels of cAMP phosphodiesterase activity.