296 strains of Listeria monocytogenes have been submitted for confirmation and further studies to the Listeria Reference Laboratory at the Institute of Hygiene in Würzburg, Federal Republic of Germany. They have been isolated between 1969 and 1985 from human cases in the Federal Republic and West Berlin. The results of an analysis of the respective cases are presented here on the basis of questionnaires. A steady increase of Listeria isolations has been noted during the past few years. The largest number of strains originated from the district Nordrhein-Westfalen which has the largest population of all German federal districts. The highest incidence calculated from the number of strains and total population was found for the district of Saarland. There was no predominance detectable of listeriosis among the rural population. 60% of the strains came from patients living in urban areas. In 6 out of 21 cases of neonatal listeriosis at least one of the parents was engaged in professional medical services. The most frequently observed clinical entities were meningitis (41.14%) and septicaemia (36.00%). Among the newborns septicaemia was predominant with 40.90%. Listeriosis during pregnancy and among newborns was connected with 53.57% of all strains isolated. The questionnaire revealed for the underlying conditions in 35% and in 24% of cases malignancies and organ transplantations, respectively. There was no increased rate of predominance found among the elderly. However, 50% of all strains isolated originated from newborns. The sex distribution was almost equal; 52.56% from males of the total number of isolates and 51.22% from males among the newborns. 67% of these which had a meningitis after the first weeks of life were male. There was no seasonal incidence detectable. Serovar 4b was found in 66.22% of all isolates tested. 295 strains produced acid from rhamnose and alpha-methyl-d-mannose, but not from d-xylose and were thus typical for L. monocytogenes. One strain needs further studies.