[en] Lymphocyte stimulation by different concentrations of phytohemmagglutinin (PHA) provided a profile of lymphocyte responsiveness in 5 normal subjects and 40 radium dial painters. This profile will, hopefully, improve detection of lymphocyte defects in patients with impairment of cellular immunity. When a suboptimal dose (0.15 μg PHA-protein) was used, decreased lymphocyte responsiveness was observed in patients with high body burdens of ²²⁶Ra (> 0.1 μCi) compared with patients with low body burdens (< 0.1 μCi) and normal subjects. At all other PHA concentrations, the lymphocyte responsiveness was not significantly different in these three groups. A decrease in lymphocyte response was found with age in both normal controls and in the radium patients, but the decrease appeared to be somewhat greater in the radium patients above 50 years of age. To test the significance of these findings, larger numbers of control subjects in the higher age groups and low body burden radium patients known not to be on any type of medication will have to be examined