Optimal conditions for the reaction of polymerization catalyzed by RNA-dependent DNA-polymerase from AMV on poly(A)- and poly(dA)-templates with d(pT)n-primers were established. Optimal concentrations of the components and pH of the reaction mixtures were found out to differ significantly. dTTP was shown to be both a nucleotide substrate and a minimal primer of the polymerization. The Km values for d(pT)2-primer (Km = 0.11 mM and 0.54 for poly(A) and poly(dA)-templates, respectively) and longer oligothymidylates were estimated. The lengthening of d(pT)n (n = 2-10) by one mononucleotide unit led to a 3-fold and 2-fold decrease of Km value for poly(A) and poly(dA), respectively. Further lengthening of the primer (n = 10-25) did not affect Km for the primers. The maximal rates of polymerization did not depend on primer length. The activation reaction (Ea = 12 kcal/mol) of polymerization on poly(A) was considerably lower than that on poly(dA) (Ea = 50 kcal/mol). In both cases a highly processive polymerization was observed. It was suggested that the synthesis had been more effective on poly(A)-template due to a more effective formation of the complex enzyme primer template.