A free standing film of polyacetylene, first obtained by Ito et al.1, has been shown by electron micrograph (EM) to consist of fibrils with average diameter of 20 nm. The results were confirmed by us2 and many other laboratories. To eliminate any morphological changes resulting from post polymerization handling of the specimen, we have developed the technique of direct polymerization onto EM grids2,3. The 20–100 nm thick polyacetylene films thus obtained were found to have 3-nm diameter microfibrils as the ultimate morphological entity which aggregate to form the more abundant 20-nm fibrils. Electron diffraction showed the polymer chain axis to be along the fibre axis3–5. In marked contrast Wegner and co-workers6–11 reported that polyacetylene particles contain irregularly shaped lamellae ∼5–20 nm in thickness connected into ribbon-like aggregates with polymer chain axis perpendicular to the aggregate direction6,7, and proposed an irregular chain folded lamellar morphology, highly cross-linked with the average length of linear chain segments of ∼20 units. We have resolved this controversial observation by reproducing the work of Wegner et al. and show here that such specimens were readily transformed to smooth fibrillar morphology by washing with methanolic-HCl.