This paper reports on the activity of bovine immunoglobulins IgG and IgG1 directed towards 19 microbial pathogens in an early milk concentrate from non-immunised cows and in a hyperimmune milk using an ELISA technique. Both products contained IgG and IgG1 which bound to all the microbial antigens tested. The early milk concentrate demonstrated a significantly higher IgG and IgG1 antibody titre (P<0.05) against all of the antigens tested than the hyperimmune milk. In addition, the early milk concentrate was shown to stimulate the accumulation of immune cells in the peritoneum of Balb/c mice.