We measured the levels of the DNA polymerases alpha, beta, and gamma in human peripheral lymphocyte cells stimulated with Tora-mame lectin (TM-lectin) and the induction patterns were compared to those with other plant lectins, i.e., phytohemagglutinin (PHA) and pokeweed mitogen (PWM). The maximum activity of DNA polymerase alpha in lymphocytes was achieved at the concentration of 10 micrograms/ml with TM lectin and the dose response curve of TM lectin showed a sharp peak in contrast to that of PWM. During prolonged stimulation for 10 days, the time course of DNA polymerase alpha induction was different among these three lectins. A peak of alpha-enzyme was correlated with maximal incorporation of [3H]thymidine and was observed on the fourth day with TM lectin, on the third day with PHA, and sixth day with PWM. DNA polymerase beta in lymphocytes was also activated by the addition of these proteins. Two different peaks were observed during a 10-day period with every lectin, and TM lectin was most potent stimulator among them. The activity of DNA polymerase gamma in lymphocytes was at a very low but detectable level which increased slightly in response to TM lectin treatment. Although some variability of gamma-enzyme activity was observed after the seventh day, the pattern in the course of 7 days was similar among the lectins.