SUMMARY Polysomes from Aedes albopictus cells were identified by their rapid labelling with radioactive amino acids and their sensitivity to EDTA, RNase and puro- mycin. The major ribosome component in cytoplasmic extracts had a sedimenta- tion coefficient of approx. 95S and may be a ribosome dimer. In Semliki Forest virus infected Aedes albopietus cells, 42S and 26S RNA were the major virus RNA species detected up to IO h post infection. Virus RNA was detected in association with pre-labelled ribosomes and banded at a buoyant density of 2.55 g/ml. 42S, 38S, 33S and 26S virus RNA species were associated with polysomes.