Verocytotoxin-producing Escherichia coli 0157:H7 (VTEC 0157:H7) was detected in two of 2446 individual faecal samples collected from pigs slaughtered at five Swedish slaughterhouses, indicating a prevalence of 0-08 per cent, with a 95 per cent confidence interval from 0 to 0.16 per cent. Four Swedish VTEC 0157:H7-pOsitiVe farms which kept ruminants and pigs were studied by repeated faecal sampling; VTEC 0157:H7 was isolated from the ruminants and pigs on all the farms and the same strains were present in the pigs and the ruminants. On one of the farms, the organism persisted in the pig population for 11 months. On all four farms, management practices which might have influenced the isolation rate in pigs were identified. A group of young VTEC 0157:H7-positive pigs was moved from one of the VTEC 0157:H7-positiVe farms to a fattening herd where there were no ruminants. The number of VTEC 0157:H7-positive faecal samples decreased gradually and after nine weeks the pigs were all negative; at slaughter none of the pigs was VTEC 0157:H7-positive.