Soluble polyadenylic acid (poly(A] polymerase content of stationary and growing cell populations from a variety of cell lines was determined. Cell populations from stationary cultures presented poly(A) polymerase values with a mean of 31 +/- 12 enzyme units/mg protein. The mean value for growing cell populations were 62 +/- 18 enzyme units per mg protein. A statistically significant difference was found between stationary and growing cell populations from the variety of cell lines examined (p less than 0.1). The observed differences in poly(A) polymerase levels persisted after fractionation of the crude extracts and revealed two molecular forms of enzyme activity with a net charge difference in stationary and growing cell cultures.