We describe the effect of HPA-23 in the DNA synthesis reaction catalyzed by DNA polymerase-alpha and reverse transcriptase. 0.085 and 0.017-mu-M of HPA-23 inhibited 50% of DNA polymerase alpha-activity in the presence of activated DNA and poly(dA)-oligo(dT), respectively. However, for reverse transcriptase, this same effect was observed only with 6.76-mu-M of the drug independently of the template-primer used (activated DNA or poly (rA)-oligo(dT)). HPA-23 was a non-competitive inhibitor with respect to activated DNA and to TTP in the DNA polymerase alpha-reaction.3441732459466