A milk immunoglobulin concentrate (MIC) containing antibodies to enteropathogenic E. coli strains was prepared by hyperimmunisation of pregnant cows and using the milk obtained during the first 6 to 8 days of lactation. The sterile concentrate contained 70 to 80% protein and 35 to 40% immunoglobulin. The antibacterial activity was measured by bacterial passive agglutination, bacteriostatic activity in vitro, phagocytic clearance in vivo, and a protection test in mice. Though differences in titers were observed, adequate immunologic activity was demonstrated by these tests. Clinical studies were performed with 60 patients (aged 10 days to 18 months) suffering from diarrhoea with isolation of enteropathogenic E. coli. They were treated for 10 days with MIC and stool cultures were done prior to, during, and 2, 3 and 4 days after termination of treatment. Among 51 patients infected with E. coli strains incorporated in the vaccine, stool cultures became negative in 43 (84.3%) after treatment with MIC and 8 remained positive. Nine patients infected with strains O 78:K80(B-) and O 114:K--(B-)--which were not included in the vaccine used for immunisation--served as controls. Only one patient in this group became negative. If all patients receiving antibiotics for non intestinal infections during the treatment period are omitted the results remained unaltered: MIC was effective in 32 out of 38 patients (84.2%). These differences were highly significant. These results provide evidence that treatment with specific MIC is effective in eliminating enteropathogenic E. coli from the intestine.