Primary encounter with antigen stimulates specific B cells not only to differentiate into cells that produce antibody at a high rate (plasma cells), but also to give rise to populations of memory cells. These cells have many characteristics that differ from virgin B cells, including their lifespan. When re-exposed to antigen, memory cells generate secondary IgG responses that are enhanced in rate, titre and affinity. At present they are considered as small resting lymphocytes which survive for long periods in a quiescent state between each antigen encounter. However, the fact that an individual may continue to make an antibody response for many months following a single injection of antigen is often overlooked. This continued antibody production is probably due to repeated stimulation of antigen-specific B cells and raises the question of whether memory B-cell clones require antigen for their maintenance. Here we show that they do, and that following transfer, in the absence of antigen, memory B-cell populations are lost from the adoptive host after 10-12 weeks.