Antibody response and generation of immunological memory in chickens after stimulation by bovine serum albumin (BSA) were investigated. A single intravenous injection of BSA induced a relatively high primary antibody response but failed to generate definite memory for the secondary antibody response. Variation in antigen dosage and the time interval between antigen injections did not affect significantly the levels of the primary and secondary antibody responses. The immunogenicity of deaggregated BSA in chickens was as potent as that of aggregated BSA. Soluble adjuvants such as the capsular polysaccharide of Klebsiella pneumoniae, cell wall lipopolysaccharide of Salmonella enteritidis and cell wall peptidoglycan of Staphylococcus epidermidis exhibited little enhancing effect on antibody response and memory. However, stimulation of chickens by BSA emulsified in Freund's adjuvant enhanced generation of memory. Repeated injection of BSA alone also showed a similar effect. It seems likely therefore that in chickens continous antigenic stimulation is required for generation of definite memory. From the present results it has been concluded that the characteristics of the immune response of chickens to BSA resemble those of mammals to T-independent antigens.