A critique of the use of DNA synthesis as a measure of the effect of mitogens on lymphocytes.

The use of DNA synthesis as a measure of mitogenic activity in lymphocytes is reanalyzed in the light of the Continuum Model, and it is suggested that although lymphocytes may have a linear response with regard to mitogen concentration, the curves using thymidine may show a threshold response at low concentrations and a decrease in activity at high concentrations.