Salmonella enterica serovar berta was isolated for the first time in Denmark in October 1984. This serovar has subsequently become endemic in the broiler industry. Plasmid profile analysis of 610 strains of S. berta isolated from broilers and broiler parent stock in the period October 1984 to July 1989 showed that plasmids were present in 85.7% of strains investigated, with a mean of 1.8 plasmids per strain. A significant increase in the mean number of plasmids per strain was seen during the observation period. Seventeen different plasmid sizes and 90 different plasmid profiles were identified. Plasmid profiling of S. berta appears to represent a promising tool for analysing the epidemiology of S. berta infections in broilers. 1991 Acta Pathologica, Microbiologica et Immunologica Scandinavica