Abstract
Highly purified T‐cell preparations are not induced by phytohaemagglutinin (PHA) to produce mitogenic factors (MF). As few as 0.1% adherent cells restore PHA induction to MF secretion. Non‐adherent, highly purified T‐cells, on the other hand, perform independently in producing MF once activated, while adherent cells are not capable of detecting MF secretion.