The yeast vacuole plays key roles in cellular stress responses. Here, we show that deletion of  lvs1 , the fission yeast homolog of the Chediak-Higashi Syndrome  CHS1 / LYST  gene, increases vacuolar size, similar to deletion of the Rab4 homolog  ypt4 . Overexpression of lvs1-YFP rescued vacuolar size in  ypt4Δ  cells, but ypt4-YFP did not rescue  lvs1Δ , suggesting that  lvs1  may act downstream of  ypt4 . Vacuoles were capable of hypotonic shock-induced fusion and recovery in both  ypt4Δ  and  lvs1Δ  cells, although recovery may be slightly delayed in  ypt4Δ . Endocytic and secretory trafficking were not affected, but  ypt4Δ  and  lvs1Δ  strains were sensitive to neutral pH and CaCl 2 , consistent with vacuolar dysfunction. In addition to changes in vacuolar size, deletion of  ypt4  also dramatically increased cell size, similar to  tor1  mutants. These results implicate  ypt4  and  lvs1  in maintenance of vacuolar size and suggest that  ypt4  may link vacuolar homeostasis to cell cycle progression.