The influence of polyamines on various enzymes involved in the excision repair pathway of DNA, such as UV endonuclease, DNA polymerase I, DNA ligase and polynucleotide kinase, and two AP-endonucleases, were studied. The polymerizing activities of DNA polymerase I and polynucleotide kinase were found to be markedly affected by polyamines. In the former enzyme the effect can be attributed to the stabilization of the correct bihelical structure at the 3' end and in the latter case polyamines stabilize the polynucleotide kinase protein itself in the correct oligomeric structure. The effect of polyamines on the hydrolysis of apurinic and apyrimidinic sites in DNA and nucleosome particles were also investigated. Spermine and spermidine were found to be the most efficient polyamines in causing such hydrolysis both in the free DNA and in the nucleosome particles.