New information is presented on the stratigraphic and geographic distribution of acritarchs of the Lower Cambrian sequences in areas around the southern margin of the Fennoscandian Shield and the Lublin Slope in the southeastern margin of the East European Platform. In the latter area a distinctive radiation of diagnostic acritarchs has been found which abruptly replaces a morphologically depleted acritarch assemblage of Late Proterozoic type from beds of theSabellidites cambriensisZone. This zone is generally regarded as basalmost Cambrian. We contend that this radiation event of algal plankters is synchronous in the investigated areas and suggest that it might be generally significant for defining the Precambrian-Cambrian boundary. The microfossil succession is set in relation to the evidently reliable trilobite-based zonation of the Lower Cambrian, which adds to their usefulness in regional correlations.