Using agarose isoelectric focusing, the isoenzymes of 19 Acanthamoeba strains were investigated. They had been isolated from nasal mucosa, and the species identification based on morphology of the cyst had previously been reported. The identification by isoenzymes differed from that by cystic morphology. Growth at 40 degrees C correlated with the species identification by isoenzymes. Six strains were identified as A. lenticulata, nine as A. mauritaniensis, one as A. rhysodes, and three belonged to the A. lugdunensis-A. quina complex. Several of the nasal A. lenticulta isolates proved to be highly virulent for mice.