Abstract: The present invention relates to a process for the manufacture of a preparation containing specific antibodies against the K-99 antigen of various strains of enterotoxigenic Escherichia coli (etec). In said process the milk obtained from postpartum cows, which had been previously vaccinated with E. coli strain 168, is clotted with a suitable enzyme. The fatty serum is then separated from the cheese obtained, the fat is then separated out, the fat-free serum is then subjected to ultrafiltration through a suitable number of appropriate membranes so that 30-50% of the water present is removed the retentate is then sterilized. Suitable membranes are those which are permeable only to molecules of less than about 22,000-30,000 daltons molecular weight. The preparation is advantageously lyophilized and the lyophilized preparation is subsequently sterilized by irridation, e.g. with Co.sup.60.