Attempts have been made to activate alveolar cells obtained by bronchoalveolar lavage from 17 patients with sarcoidosis in different stages with the lectins concanavalin A and leukoagglutinin. The cells obtained from 2 of the patients responded well by proliferation whereas the cells from the other 15 patients responded poorly. Coculture experiments indicate that the low proliferative response was not due to inhibitory effects exerted by alveolar lymphocytes or macrophages, but rather to a lack of responding T cells. The results are discussed in relation to other studies showing increased immune reactivity in alveolar lymphocytes from patients with sarcoidosis.