One hundred and seven strains of Listeria monocytogenes isolated from human cases of listeriosis in Sweden during 1976-1985 were investigated. Sero- and phagetyping showed that 74 strains (69%) belonged to serovar 4b and that 47 of these strains also shared phagovar 2389:2425:3274:2671:47:108:340. Strains sharing this phagovar were further analyzed by REA, and could accordingly be arranged into five REA groups. However, the majority of the 47 strains were distributed in two of the groups. This indicates that two clones of L. monocytogenes were responsible for a major part of the human cases of listeriosis in Sweden during the ten-year period studied.