Previous studies on the resistance of yeast cells to dehydration pointed towards the protective role of trehalose and the importance of the specific trehalose transporter in guaranteeing survival. The present report demonstrates that the trehalose transporter is essential during the germination process in order to translocate trehalose from the cytosol to the external environment. Diploids that lack the trehalose transporter germinate poorly and do not form 4 spore tetrads although they accumulate trehalose and show trehalase activity. Furthermore, addition of exogenous trehalose to the germination medium enhances germination and normal segregation. The ability to transport trehalose is dominant and seems to be related to a single gene.