Isoenzyme electrophoresis of three different enzymes was used to compare 16 strains of vahlkampfiid amoebae and a strain identified as a slime mold. The strain designated as an Echinostelium sp. was found to be an isolate of Naegleria fowleri on the basis of zymogram type and other characters, confirming Cursons & Brown's similar conclusion drawn in 1975. The N. fowleri strains examined expressed the typical zymograms of the species. The N. gruberi strains in this study presented two distinctive groups of patterns that were different from the two previously reported types for N. gruberi. Each of the remaining species studied formed single distinctive groups by which they could be identified.