The transition effects in the 2 mm and induced spin echo of the 3-cm ESR ranges have been used to study the relaxational parameters of neutral and modified (with irradiation and doping) polyacetylene. Times of spin-spin and spin-lattice relaxation of cis- and trans-polyacetylene have been determined for the 90-320 K temperature range. The dependence of these parameters on the sample thickness, digree of pi-conjugation and concentration of paramagnetic centres is shown. The square dependence of the rate of spin-lattice relaxation on temperature points out the predomination of the Raman relaxational processes in a polymer. Irradiation results in stabilization of polyacetylens parameters