Abstract: The complete nucleotide sequence of a 40.7 kb segment about 130 kb from the left end of chromosome X of Saccharomyces cerevisiae was determined from two overlapping cosmids. Computer analysis of that sequence revealed the presence of the previously known genes VPS35, INO1, SnR128, SnR190, MP12, YAK1, RPB4, YUR1, TIF2, MRS3 and URA2, three previously sequenced open reading frames (ORFs) of unknown function 5' of the INO1, 5' of the MP12 and 3' of the URA2 genes and 13 newly identified ORFs. One of the new ORFs is homologous to mammalian glycogenin glycosyltransferases and another has similarities to the human phospholipase D. Some others contain potential transmembrane regions or leucine zipper motifs. The existence of yeast expressed sequence tags for some of the newly identified ORFs indicates that they are transcribed. A cluster of six genes within 10 kb (YUR1, TIF2, two new ORFs, an RSP25 homologue and MRS3) have homologues arranged similarly within 28.5 kb on the right arm of chromosome XI.