Quantitative processing of large numbers of phytoplankton collections requires a sampling method that will yield precise and reproducible estimates of abundance within an acceptably short counting time. A two‐stage sampling plan was developed, using the Sedgwick‐Rafter cell, which satisfies these criteria. The sampling design is appropriate for larger phytoplankton species (> 10–15 µ) having relatively high population densities (⩾ 105 cells/liter) .