Candida parapsilosis is an important human pathogen, responsible for severe cases of systemic can-didiasis and one of the leading causes of mortality in neonates. In this report, we describe the first system for genetic manipulation of C. parapsilosis. We isolated and subsequently determined DNA sequences of genes encoding galactokinase (CpGALl) and orotidine-5′-phos-phate decarboxylase (CpURA3) from a genomic DNA library of C. parapsilosis by functional complementation of corresponding mutations in Saccharomyces cerevisiae. The predicted protein products, Gallp and Ura3p, displayed a high degree of homology with corresponding sequences of C. albicans and S. cerevisiae, respectively. A collection of galactokinase-deficient (gall) strains of C. parapsilosis was prepared using direct selection of mutagenized cells on media containing 2-deoxy-galac-tose. Additionally, we constructed a plasmid vector carrying CpGALl as a selection marker and a genomic DNA fragment with an autonomously replicating sequence activity that transforms the C. parapsilosis gall mutant strain with high efficiency. This system for genetic transformation of C. parapsilosis may significantly advance the study of this human pathogen, greatly improving our understanding of its biology and virulence, with implications for drug development.