Stimulation of the proliferation of chicken fibroblasts by folic acid or a serum factor(s) in a plasma-containing medium.

The proliferation of chicken fibroblasts is strongly stimulated by folic acid, at greater than physiological concentrations, in a plasma-containing medium, or by serum in a medium of physiological folic acid concentration. Serum and plasma, however, do not appear to differ in their content of folic acid derivatives.A qualitative difference between the proliferative behaviors of normal and transformed fibroblasts is obtained when these cells are cultivated in a physiological-folate-low-calcium-plasma medium. In such a medium, transformants proliferate steadily, at a significant rate, while normal fibroblasts do not multiply at all.