Anyone who followed the developing epidemic of Severe Acute Respiratory Syndrome (SARS) in the media would be in little doubt as to the threat posed by new and unexpected diseases. Whilst the general public is probably more familiar with the various ′exotic′ viruses that have emerged in the past thirty years, medical mycology also has its own share of important emergent pathogens. In a regional context the most important of these is Penicillium marneffei Segratin et. al. – the causative agent of penicilliosis. This has become a very important complication in AIDS patients in large parts of the Far East, particularly in Thailand, Southern China and Hong Kong. Unlike more familiar fungal pathogens, such as Candida albicans and Aspergillus fumigatus, P. marneffei has only a short history – indeed it was first described as recently as the mid-1950s.