Abstract: To study the effect of the ret1-1 mutation on the secretome, the glycosylation patterns and locations of the secretory proteins and glycosyltransferases responsible for glycosylation were investigated. Analyses of secretory proteins and cell wall-associated glycoproteins showed severe impairment of glycosylation in this mutant. Results from 2D-polyacrylamide gel electrophoresis (PAGE) indicated defects in the glycosylation and cellular localization of SDS-soluble cell wall proteins. Localization of RFP-tagged glycosyltransferase proteins in ret1-1 indicated an impairment of Golgi-to retrograde transport at a non-permissive temperature. Thus, impaired glycosylation caused by the mislocalization of ER resident proteins appears to be responsible for the alterations in the secretome and the increased sensitivity to ER stress in ret1-1 mutant cells.