A fluorescence antibody test with monoclonal antibodies was used to determine the subgroup (A or B) of respiratory syncytial virus from infants hospitalized in Caen, France, over eight consecutive epidemics from 1982 to 1990. From 1982 to 1985, 27 (30%) out of 90 frozen nasal slides were classified as subgroup A strains and 63 (70%) were classified as subgroup B. B strains predominated over A in 1983-1984 and 1984-1985. From 1985 to 1990, 284 respiratory syncytial virus field strains were reisolated from frozen materials; 115 (40.5%) were typed as subgroup A and 169 (59.5%) were typed as subgroup B. In 1985-1986, 1986-1987, and 1988-1989, both subgroups were present in almost equal numbers; subgroup A (88.3%) predominated in 1987-1988, and subgroup B (84.5%) predominated in 1989-1990. In conclusion, both subgroups occur together each year, and one subgroup rarely predominates, e.g., subgroup A in 1987-1988 and subgroup B in 1983-1984 and 1989-1990. Therefore, there is a gradual change of the predominant subgroup into another over a period of about 5 years; the relative frequency of subgroup A strains increased from 1983 to 1988, whereas the percentage of subgroup B decreased during the same period.