Antigen-specific serum antibodies are protective for long periods of time 1, 2. These serum antibodies, the "humoral memory", are secreted by plasma cells derived from activated, antigen-specific B lymphocytes. Given their crucial role in immunity, surprisingly little is known about the biology of plasma cells. One of the fundamental questions is whether persisting protective serum antibody responses are maintained by long-lived plasma cells, or by short-lived plasma cells generated continuously from activated memory B cells. Here, we review some recent experiments suggesting that plasma cells have the capacity to live for unlimited time if rescued by specific factors provided in a limited number of survival niches in the body.