In this study we evaluated the release of leukotriene B4 (LTB4) in the cerebrospinal fluid (CSF) of 12 patients with Acquired Immunodeficiency Syndrome (AIDS), which disease was complicated by Cryptococcal Meninigitis and in CSF of 12 control subjects with inflammatory and degenerative pathologies of the Central Nervous System (CNS). We obtained low levels of LTB4 in all the AIDS patients (mean 60.5 pg/ml), while the HIV negative subjects with degenerative and inflammatory pathologies of CNS showed a mean of 91.5 pg/ml. The finding of low levels of this inflammatory reaction mediator agrees with the limited clinical symptoms of cryptococcal meningoencephalitis in patients affected by AIDS.