We investigated the state of humoral and cellular immunity of 16 patients (eight women, eight men, aged 16 to 80 years), who had suffered from extraintestinal manifestations of infections with enteritis salmonellae. Four patients were examined during the acute state of the disease, the others one to three years thereafter. These patients were in good clinical condition. In all cases we could exclude an antibody deficiency syndrome. In the peripheral blood of 11 patients, we found a diminished number of T-helper lymphocytes, mostly together with a decrease in total T lymphocytes. Because the microbicidal activity of macrophages may be impaired by a general or localized decrease in T-helper cells, we suggest that the phagocytized enteritis salmonellae survive in this way and cause the atypical course of the infection in these patients.