Abstract A healthy 15-year-old girl suffered fatal meningoencephalitis due to free-living amebas identified as naegleria. The organisms were cultured from cerebrospinal fluid, brain, lung, liver and spleen, and were seen in heart blood. Acute, diffuse myocarditis complicated by pulmonary edema occurred and was believed to be related to the infecting amebas. Primary amebic meningoencephalitis is being recognized with increased frequency and appears to be worldwide and capable of producing epidemics. Patients often give a history of swimming in fresh or brackish water, and the portal of entry may be the nasal mucosa. By means of appropriate technics, isolation of free-living amebas is relatively simple. All isolates (Florida, Virginia, Australia and Czechoslovakia) have been naegleria. The disease appears to be universally fatal and at present without promise of therapy.