The phytoplankton species diversity was rather high in the Skagerrak and Kattegat areas although the number of cells was higher in the latter. Diatoms dominated the samples and chlorophyll a concentrations were at average at all stations but somewhat enhanced, within the limits, at Å13 in the Skagerrak and at Fladen in the Kattegat area. Small flagellated species dominated at the Baltic stations. The flagellate Chrysochromulina polylepis was present at most of the stations and was quite numerous at BY38. The integrated (0-20 m) chlorophyll a concentration was just above average at BCSIII-10 and within average at all other stations in the Baltic.