Yeast revealed to be a versatile organism for studying endocytosis. Here, inhibition of endocytosis by H(2) O(2) and its correlation with apoptotic cell death were ascertained in Saccharomyces cerevisiae. We found that H(2) O(2) causes alterations in vacuolar morphology and a concentration-dependent inhibition of endocytosis. We also found that H(2) O(2) -induced endocytosis inhibition is a reversible process that occurs in the early phase of the apoptotic cascade, preceding chromatin condensation and DNA fragmentation. Additionally, mutants affecting early steps of the endocytic pathway display sensitivity to H(2) O(2) . As endocytosis inhibition was also observed with acetic acid, it may be a broader cellular dysfunction of oxidative stress-induced toxicity in yeast.