1. Spermine, spermidine and putrescine activated DNA-dependent DNA polymerase from human sera by 47-125% at the concentrations of 0.2, 3 and 30 mM, respectively. 2. The polyamines shifted the optimal MgCl2 concentration for the polymerase activity from 10 mM to more physiological 5 mM. 3. Histamine having amino and imino groups at both ends of the molecule also increased the DNA polymerase activity, while cyclopentylamine and n-butylamine showed no effects on the enzyme activity. 4. The stimulatory effect of polyamines on the DNA polymerase activity was more evident with poly(dC)p(dG) used as a template/primer than with poly(dA)p(dT).