Immunological typing of 15 Japanese encephalitis (JE) virus strains was done by HI and AGDP tests with preliminary cross adsorption of antibodies with antigens, observing standard quantitative adsorption conditions. Most of the strains (12) were found to belong to the immunological type Jagar-01, including the strains isolated in the USSR, Korean People's Democratic Republic, most strains isolated in Japan (6 out of 7) and Chinese People's Republic (3 out of 4). The Hanoi-60 strain isolated in Socialist Republic of Vietnam belongs to the Nakayama immunological type. A correlation was shown between strain grouping by the immmunological type and genetic markers (hemagglutinin thermoresistance at 42 degrees C/20 min and optimal pH range for HA test). Two strains were found to represent transitional variants between the above two immunological types.