One accidental and 17 natural human infections caused by Penicillium marneffei have been reported in the literature. The accidental infection, in Paris, followed inoculation of a culture from a Vietnamese bamboo rat into the finger of a mycologist. All patients with natural infections had lived or traveled in the Far East. Nine of these patients were Chinese, all from Guangxi Zhuang Autonomous Region. The four additional infections from Guangxi reported herein bring the total to 21 natural infections. P. marneffei is a primary pathogen of humans, causing two clinical types of disease: focal infection and fatal, progressive, disseminated infection. There are three histopathologic reactions: (1) granulomatous; (2) suppurative; and (3) anergic and necrotizing. The first two reactions are seen in patients with "normal" immunity and the third in patients with compromised immunity. P. marneffei is unique among species of Penicillium because of its thermal dimorphism, its recognized ecologic niche (restricted to the Far East), and its propensity to infect the lungs and the reticuloendothelial system and to proliferate within histiocytes.