Abstract
Negative staining electron microscopy was used to examine culture fluids from the H9/HTLV-III cell line after concentration by centrifugation. Characteristic retrovirus-like particles bearing distinctive envelope projections were seen. The virion envelope was frequently extended in the form of a bleb or a tail. These particles were morphologically virtually indistinguishable from similar preparations of Friend murine leukaemia virus. H9/HTLV-III culture fluids contained, in addition, numerous comet-shaped particles with a dense head and flared tail. These particles were clumped by the addition of anti-HTLV-III-positive serum suggesting that they may represent intermediate forms of the virus.