Abstract: Antigen specific excreted transfer factor may be obtained by collecting material, e.g. colostrum or milk, secreted by the mammary gland of a suitable lactating mammal, e.g. a cow having immunity to the antigen under suitable conditions such that materials which interfere with transfer factor efficacy are removed so as to obtain transfer factor. Colostrum or milk so collected may be used directly, typically after sterilization, or may be treated to further concentrate and/or purify transfer factor. Treatment to yield colostral whey containing transfer factor is presently the preferred method for obtaining transfer factor for use in conferring immunity against diseases associated with antigens for which the transfer factor is specific. Cell-associated transfer factor specific for an antigen may also be obtained by incubation release from, or lysis of, cells obtained from the collected material.