Since 1987, the number of cases of salmonellosis caused by Salmonella enteritidis has considerably increased in Western Europe. Comparison of endemic animal strains isolated in Belgium from 1976-84 with strains isolated from 1987 on shows that the strains which cause the current epidemic have no features distinguishing them from the previously-isolated strains and that furthermore, they do not constitute a bacterial clone. They belong to 13 different lysotypes and in most cases remain sensitive to antibiotics. Nevertheless, the lysotype 33 (which belongs to the phage type 4 has increased significantly. It encompasses 37% of the animal strains isolated in Belgium from 1987-9, but only 7% of the strains isolated from 1976-84. It is worth noting that the endemic as well as the epidemic strains contain a virulence plasmid sharing sequence similarities with the FIB and FIIA plasmid replicons and with the VirA and VirB virulence regions of the S. typhimurium virulent plasmid: pIP1350.