Degenerate oligonucleotides (derived from conserved regions of PLB1 genes from S. cerevisiae and other fungi) were used to amplify PLB1 homolog fragments from C. albicans and C. tropicalis by using the polymerase chain reaction. The C. albicans PLB1 fragment was then used as a probe to clone the full-length gene and to monitor PLB1 mRNA expression. The C. albicans PLB1 gene consists of a 1815-bp open reading frame encoding a putative protein of 605 amino acids. It contains the highly conserved Gly-X-Ser-X-Gly catalytic motif, found in all lipolytic enzymes, and exhibits significant homology with other fungal PLB1 gene products (approximately 63% similarity, approximately 45% identity). Blastospores and pseudohyphae expressed higher levels of PLB1 mRNA than germ-tube-forming cells. TUP1, a general transcriptional repressor, may regulate PLB1 expression in C. albicans, since PLB1 expression was the highest in tup1 delta mutants and did not vary in response to environmental stimuli. Together, these results suggest that expression of the C. albicans PLB1 gene is regulated as a function of morphogenic transition.