Genetic transformation of a biological oxygen demand (BOD)-sensing yeast, Trichosporon cutaneum IFO 10466 was carried out using a plasmid shuttle vector, pAN 7-1, between Escherichia coli and Aspergillus niger and Aspergillus nidulans. The hygromycin B-resistant transformants were obtained with the plasmid by using the spheroplasts. The transformation frequency was up to 70 colonies per mu g of plasmid DNA. Southern-blot analysis and transformation test of E. coli using DNA extracts from hygromycin B-resistant transformants of IFO 10466 indicated that pAN 7-1 existed independently in the cells without integration into the chromosome. These results suggest that pAN 7-1 has potential availability for introduction and expression of the external gene such as a bioluminescence gene, lux or luc, to create a luminous yeast for BOD sensing.