The index of infection (the number of positive samples to the total number of investigated samples ratio) was used to study the intensity of the inapparent epizootic process in avian salmonellosis. Two flocks of broiler birds were followed up for the presence of Salmonella organisms over the period of hatching up to the end of fattening. The study of samples taken from the cloaca revealed a high index of infection (15 to 31.7 per cent) among the clinically normal birds. Two laboratory tests were carried out to confirm the results. Sixteen, resp., 26 day-old, Salmonella-free birds were kept together with 2 (in each group) birds orally infected with S. isangi. Up to the 13th day (the end of the experiment) the percent of the infected contacts reached 92.3 and 100. This made it reasonable to believe that there was a chain of infections following one after an other among healthy birds maintained by sources of Salmonella organisms--an inapparent epizootic process.