Synthesis of multiple extracellular lipases in Candida rugosa has been demonstrated. However, it is difficult to characterize the expression spectrum of lip genes, since the sequences of the lip multigene family are very closely related. A competitive reverse transcription-PCR assay was developed to quantify the expression of lip genes. In agreement with the protein profile, the abundance of lip mRNAs was found to be (in decreasing order) lip1, lip3, lip2, lip5, and lip4. To analyze the effects of different culture conditions, the transcript concentrations for these mRNA species were normalized relative to the values for gpd, encoding glyceraldehyde-3-phosphate dehydrogenase. In relative terms, lip1 and lip3 were highly and constitutively expressed (about 10(5) molecules per microg of total RNA) whereas the other inducible lip genes, especially lip4, showed significant changes in mRNA expression under different culture conditions. These results indicate that differential transcriptional control of lip genes results in multiple forms of lipase proteins.