Abstract. Well-preserved acritarchs and prasinophyte algae recovered from the Lower Wenlock of Gotland (Sweden) were used to test the effects of centrifuging in heavy liquid, treatment with nitric acid to remove pyrite, and the loss of material through a 7 μm sieve during washing of a sample. The centrifuge test showed that the relative proportions of different genera stabilized after three heavy liquid separations and the number of acritarchs extracted fell consistently by about 35% at each separation. Treatment with nitric acid yielded a slightly lower number of acritarchs per gram of sediment, but it appears to have yielded more herkomorph and sphaeromorph acritarchs. Treating samples with nitric acid renders them more comparable with those not containing pyrite. The loss of specimens whilst washing through a 7 μm sieve proved to be minimal. It was concluded that three heavy liquid separations should routinely be carried out, in conjunction with treatment with nitric acid and regular tests to examine material passing through a 7 μm sieve.