A total of 1602 stool samples from healthy employees in a slaughter company were screened by PCR for Shiga toxin (Stx)-producing Escherichia coli (STEC). The PCR product of Stx-encoding genes was detected in 90 (5.6%) of 1602 stool samples. Among the 90 stx-positive workers, the Residual Products Handlers and Slaughterers had rates of 8.0% and 6.0%--higher than Inspectors, Grading Testers and Livestock Hygiene Controllers at 3.3%, 2.0% and 3.5%, respectively. Forty-nine (54.4%) were shown to have stx2; 25 (27.7%) carried stx1 and 16 (17.7%) had both stx1 and 2. Distribution of the stx PCR-positive workers by age revealed an increase in STEC infection with age (P<0.05). Phenotypic and genotypic traits of nine STEC strains isolated from eight slaughter plant workers were characterized. A variety of serotypes, five O serogroups (O8, O54, O59, O103 and O153) and two H serogroups (H7 and H32) were found, but none of the strains belonged to the serogroup O157. Eight Vero cell cytotoxicity assay-positive strains were isolated from the workers and these workers were asymptomatic and healthy. The results of the study show that slaughter plant workers are at high risk of STEC infection.