Peripheral blood T and non-T lymphoid cells were examined in 31 patients with a variety of primary immmunodeficiencies for their locomotor activity toward casein and endotoxin-activated serum. T cells from 1 and non-T cells from 2 of 7 patients with Bruton type agammaglobulinemia had poor locomotor activity in this system. Both T and non-T lymphoid cells from all patients with common variable immunodeficiency disease had normal locomotor response to casein and EAS. Heterogeneity in locomotor abnormaltiy of T and non-T cells toward casein and endotoxin-activated serum was observed in other immunodeficient patients. No direct correlation was observed between the proportion of cells in the several T cell subsets and the abnormalities of locomotion of T cells.