Penicillium marneffei was isolated from three blood cultures of a Thai woman with AIDS and then identified as such. The patient, 41 a year-old female from northeast Thailand came to Japan 10 years ago and married a Japanese man. She was reportedly the third patient infected with this fungal species in Japan, and considered to be the first case from whom the causative fungus was successfully cultured, which led to the diagnosis of penicilliosis marneffei. The colony of the isolate, which was cultured on Sabouraud dextrose agar at 25-27 degrees C, was initially white and pannose, gradually turned in color from yellow to yellow-green, and diffused a deep red pigment into the medium. Conidial heads were divergent, and chains of conidia were formed from phialides. Colonies of the isolate, which was cultured on brain-heart infusion agar at 35 degrees C, had a grayish white, membranous yeast-like form with fine plicae and microscopically consisted of short hyphae. Furthermore, 560 bases of the internal transcribed spacer (ITS) region of the ribosomal RNA gene including the 5.8S region (ITS1-5.8S-ITS2) (DDBJ accession number AB298970) were sequenced and allowed an unequivocal species identification.