The 19S outer arm dynein of trout sperm flagella is a complex of proteins composed of two heavy chains, five intermediate chains and at least six light chains. After dialysis against a low ionic strength buffer, its beta subunit was purified and used to generate a rabbit polyclonal antibody. This polyclonal antibody reacted strongly with the trout beta dynein heavy chain (DHC) but not with the trout alpha dynein heavy chain; it also recognised the dynein intermediate chains and tubulins. A specific antibody directed against the beta DHC was obtained by blot-affinity purification. This specific anti-trout beta DHC reacted with the beta DHC from the sea-urchin sperm 21S dynein and also with one heavy chain (> 400 kDa) of demembranated ram sperm. This anti-beta DHC antibody, and also the whole polyclonal, did not react with heavy chains in trout brain or liver extracts, sheep brain extract or purified brain and testicular cytoplasmic dyneins. These results suggest that a specific epitope of one of the sperm outer arm dynein heavy chains is conserved throughout evolution and that this epitope is not present on cytoplasmic dynein.