Abstract The kinetics of reduction (n doping) of fibrillar films of polyacetylene (PA) by a large excess of organoalkaline electron donors in solution was studied. The doping rate is proportional to dopant concentration and inversely proportional to the square of film thickness (in a range 100–1000 microns). This means that the kinetics of reduction is entirely controlled, in these experiments, by the interfibrillar diffusion of dopants, leading to macroscopic doping inhomogeneity if the reaction is stopped before completion. The maximum doping level achieved at the end of the reaction is mainly controlled by the redox potential of the dopant. Homogeneously doped thick films, at various doping levels, were prepared using a suitable set of dopants in various solvents.