Diatoms in cores from four Greenland lakes are reported; one lake is situated in NE Greenland, two in NW Greenland, and one in W Greenland. All cores are of postglacial age, the earliest sample radiocarbon-dated to c. 8500 B.P.; in each core the latest sample is taken a few cm below the lake bottom.

Previously investigated cores from Greenland showed a gradual change of environmental pH from alkaline to faintly acid lacustrine environments. This is also the case at one of the two sites in NW Greenland, and in W Greenland the pH is initially alkaline but subsequently developing towards neutral and slightly below it. At Station Nord, NE Greenland, the pH is faintly alkaline. However, the data from the fourth lake. Qeqertat, NW Greenland is rather confusing, as the alkaline environment which seems to persist is suddenly interrupted three times by higher levels of acidity.

The diatom flora consists predominantly of cosmopolitan species which are mostly recorded from the extant Greenland flora. In some aspects it represents a transition between the flora of northern Europe and North America. Most of the taxa are recorded from both regions, but some seem to be more common in Europe, whereas a few are more common, or previously only found in North America, especially Alaska.

Some species of particular interest are commented upon, and photographs of selected species are included.