Three distinct bands with high electrophoretic migration rates were isolated and purified from rainbow trout seminal plasma. The molecular masses of these bands were determined to be 5158.8, 4065.9 and 4929.0 Da. The N-terminal amino acids sequences were elucidated and were found to have high homology with Atlantic salmon apolipoprotein C-I. It can be concluded that apolipoprotein C-I is a major component of rainbow trout seminal plasma. Further studies are necessary to confirm the protective effects of apolipoprotein C-I on spermatozoa in terms of the stabilisation of the sperm membrane.