The study of gene regulation in many organisms has been facilitated by the development of reporter genes. The authors report the use of lacZ from Streptococcus thermophilus, a gene encoding a beta-galactosidase, as a reporter for the fungal pathogen Candida albicans. As test cases, Strep. thermophilus lacZ was placed under control of three different C. albicans promoters: MAL2 (maltase), inducible by maltose; HWP1 (hyphal cell wall protein), induced by conditions that promote filamentous growth; and ACT1 (actin). These constructs were each integrated into the C. albicans genome and beta-galactosidase activity was readily detected from these strains, but only under the appropriate growth conditions. Beta-galactosidase activity could be detected by several methods: quantitative liquid assays using permeabilized cells, colorimetric assays of colonies replicated to paper filters, and in situ coloration of colonies growing on medium containing the indicator X-Gal. These results show the usefulness of STREP: thermophilus lacZ as a monitor of gene regulation in this medically important yeast.