We have studied humoral and cell immunity in 14 children, from 2 months to 15 years old, diagnosed with Langerhans cells histiocytosis who had not received immunosuppressant nor immunopotentiating treatment. At the time of diagnosis, children were found in the following Greenberger clinical stages: stage II (5), stage III (6), stage IV (3). The children in stage II had moderate alterations in immunity, with an increase in IgG, IgM, IgA, increase in T4 lymphocytes and decrease in T8 lymphocytes; the clinical evolution was good. In stage III, normal immunoglobulins were noted in 2 children, an increase in IgG, IgM, IgA in 1; an increase in IgM in 1, a decrease in IgM in 1 and absence of IgA in 1. In all a decrease was found in T8 lymphocytes and the T4 lymphocytes were decreased in 3 and normal in 3; delayed immune response and response to mitogens was decreased in 3. These findings were related to a bad prognosis; 2 children died and another developed chronic disease. In stage IV serious alterations were detected in the immune system with a decrease in IgG, IgM, IgA, an increase in IgE, a decrease in T, B, T4 and T8 lymphocytes and very slight delayed immune response and response to mitogens; the children died.