Abstract: Dictamnine, a natural plant product, has been reported to have antimicrobial activity against bacteria and fungi; however, the dictamnine response mechanisms of microorganisms are still poorly understood. We have shown that dictamnine has antimicrobial activities against the model fungus Saccharomyces cerevisiae, with a minimum inhibitory concentration (MIC) value of 64 microg/ml. Commercial oligonucleotide microarrays were used to determine the global transcriptional response of S. cerevisiae triggered by treatment with dictamnine. We interpreted our microarray data using the hierarchical clustering tool, T-profiler. Several major transcriptional responses were induced by dictamnine. The first was the induced environmental stress response, mainly under the control of the Msn2p and Msn4p transcription factors, and the repressed environmental stress response in genes containing the PAC (RNA polymerase A and C box) and rRPE (ribosomal RNA processing element) motifs. The second was the Upc2p-mediated response involved in lipid biosynthesis. The third comprised the PDR3- and RPN4-mediated responses involved in multidrug resistance (MDR). Finally, the TBP-mediated response was induced with dictamnine treatment. TBP is an essential general transcription factor involved in directing the transcription of genes. Quantitative real-time RT-PCR was performed on selected genes to verify the microarray results. Furthermore, morphological transitions during dictamnine exposure to S. cerevisiae L1190 (MATa/alpha) were examined, using confocal laser microscopy. Copyright (c) 2008 John Wiley & Sons, Ltd.