Pollen analyses of Late Quaternary sediments from nine marine piston-cores reveal a continuous vegetation and environmental record for eastern Indonesia and northern Australia. On the island of Halmahera a montane oak forest largely replaced the tropical lowland vegetation during the last glacial period, while fern cover was strongly reduced during its maximum (18,000 yr B.P.). Climate was cooler and slightly drier than today. Around 10,000 yr B.P. mangrove vegetation expanded following the rising sea-level. In our western new Guinea record, at 14,000 yr B.P. climate grew warmer and slightly wetter, until it stabilised around 10,000 yr B.P. At that time the mid- to upper montane forests expanded to their full altitudinal range and fern cover increased, while montane oak forest, grassland and woodland areas had contracted. In our marine pollen records, during the last glacial the climate of northern Australia was distinctly drier than today. Grassland vegetation with sedges increased considerably at 38,000 and 24,000 yr B.P. replacing eucalypt forest and culminating in a maximum grassland cover at the height of the last glaciation (18,000 yr B.P.). The rapid sea-level rise allowed the expansion of mangrove forests and salt-bush marshes which had become established on the large tidal flats of the drowning Sahul Shelf, around 12,000 yr B.P. One piston-core (G6-4) extends to 300,000 yr B.P. and shows that glacial periods are characterized by high pollen concentrations in marine sediments, recording expanding grassland vegetation. During interglacial woodland and fern cover increased, while pollen concentrations in the sediments were low. After 190,000 yr B.P. a more open vegetation suggests that conditions were in general much more arid than before. Repeated mangrove vegetation expansions suggest major rises in sea-level at around 244,000, 220,000 and 130,000 yr B.P. © 1991.