The organism constantly requires nucleotides, especially for tissues that present a high rate of turnover, such as the cells of the immune system. In certain circumstances, nucleotides may become semi-essential nutrients required by a particular organ. There is evidence of the potential role of exogenous nucleotides as regulators of the immune function. In experiments carried out with animals, studies have shown that dietary nucleotides stimulate the humoral immune response to T-dependent antigens and raise total antibody levels. The present study reveals an increase in the production of immunoglobulins, an improved response to vaccines, a reduction in morbidity and increased tolerance to dietary antigens. Therefore, the addition of nucleotides to formula appears to favour the immune function. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.