Acetaldehyde is a toxic compound produced by Saccharomyces cerevisiae cells under several growth conditions. The adverse effects of this molecule are important, as significant amounts accumulate inside the cells. By means of global gene expression analyses, we have detected the effects of acetaldehyde addition in the expression of about 400 genes. Repressed genes include many genes involved in cell cycle control, cell polarity, and the mitochondrial protein biosynthesis machinery. Increased expression is displayed in many stress response genes, as well as other families of genes, such as those encoding vitamin B1 biosynthesis machinery and proteins for aryl alcohol metabolism. The induction of genes involved in sulfur metabolism is dependent on Met4p and other well-known factors involved in the transcription of MET genes under nonrepressing conditions of sulfur metabolism. Moreover, the deletion of MET4 leads to increased acetaldehyde sensitivity. TPO genes encoding polyamine transporters are also induced by acetaldehyde; in this case, the regulation is dependent on the Haa1p transcription factor. In this paper, we discuss the connections between acetaldehyde and the processes affected by this compound in yeast cells with reference to the microarray data.Ministerio de Educación y Ciencia (CICYT ALI99-1224-002-C02 and CICYT AGL2002-01109)