The technique involved in studying the activation of lymphocytes in the resting form, and their recognition as dividing and functional cells was studied, using phase contrast and agar as well as fluid culture. Standardization of technical methods was found to be essential, and the effect of variables was studied. Lymphocytes from human umbilical cord vein blood were found to be spontaneously activated. Infestation by microfilaria either diminished or entirely inhibited activation. The significance of lymphocytic cohesion was considered and the formation of colonies of activated lymphocytes on agar is described. The effects of non-human vertebrate lymphocytes and of human cells other than lymphocytes were studied. Spontaneous activation of abnormal lymphocytes was noted.