The lithostratigraphy of a section exposed at Sel Ayre on the Walls Peninsula, Shetland Mainland is described. A peat bed 50 cm thick is overlain by 7·3 m of sands, gravels, and boulder clay. Pollen analyses of this peat bed and of peat laminae in the sands reveal three distinctive pollen assemblages. These assemblages are interpreted as reflecting a vegetational development from grass- and fern-dominated communities an fertile brawn-earths to dwarf-shrub heaths dominated by ericaceous shrubs including Bruckenthatia spiculifolia. These heaths grew on acid humus-rich podsols and were replaced by open, grass-dominated communities. Numerical comparisons of the Sel Ayre pollen spectra with pollen data from other sites on Shetland using principal components analysis suggest that three interglacial stages are represented on Shetland Mainland –Fiandrian, Ipswichian and Hoxnian. On the basis of the composition of the presumed long-distance tree-pollen rain, the Sel Ayre sequence is correlated with the Ipswichian stage. A basic interglacial cycle is proposed for the Shetlands.