Comparative testing was carried out on a farm with 2 live vaccines against coli bacteriosis . Studied were blood and milk sera taken from test and control pigs and blood sera from pigs born by them. Both the test and control groups were clinically followed up with recording the morbidity and mortality indices. It was found that the titer of the K88 antibodies rose after vaccination with the two vaccines and retained its level up to the 30th day after farrowing. The titer of the O antibodies remained unchanged or rose negligibly after vaccination. The pigs of the vaccinated sows had higher titers of the K88 antibodies as against those of the untreated sows. Sows treated with live vaccines against coli bacteriosis transmitted antibodies through the colostrum and milk to the pigs born by them. The passive immunity acquired led to the prolongation of the incubation period of the disease and to lowering both the morbidity and the mortality of pigs.