Abstract: In the frame of the European Network for Functional Analysis (EUROFAN) we have deleted 18 yeast open reading frames (ORFs) from chromosomes II, X and XIV using the short flanking homology-PCR strategy. Two diploid strains were used: FY1679 and CEN.PK2. The deletion kanMX6 cassettes with long flanking homology and the cognate gene clones have also been constructed. Heterozygous diploid deletant strains have been sporulated. Tetrad analysis revealed that all the ORFs studied were non-essential. However, four deletant strains exhibited phenotypes. The YBL025w delta strain showed extremely slow cellular growth under all conditions tested. The YJL204c delta strain grew slower than wild-type at 30 degrees C and 37 degrees C, was cold-sensitive, and the homozygous diploids did not sporulate. The YNL213c delta strain did not grow on glycerol and had lost mitochondrial DNA. The deletion of YNL215w caused slower growth on all media but the defect was more pronounced on glucose-minimal and glycerol-rich media than on glucose-rich medium. All deletion mutants were complemented by the corresponding plasmid borne cognate gene. The YJL204w, YNL213c and YNL215w ORFs do not bear significant homology to proteins of known function. YBL025w has recently been identified as RRN10, a gene that encodes an RNA polymerase I-specific transcription initiator factor. The deletion of the remaining fourteen ORFs did not reveal any mutant phenotype in our basic growth tests.