A two-dimensional polyacrylamide gel electrophoresis map of bull seminal plasma proteins has been established. About 250 spots were detected after silver staining and polypeptides from 24 spots have been N-terminally sequenced. Major proteins already described in bull seminal plasma, like PDC-109 and aSFP, have been located on the map; proteins not yet reported in male reproductive tracts have been evidenced; for some polypeptides showing a previously unknown N-terminal sequence, structural similarities with proteins described in other organisms have been found. A reference map of seminal plasma proteins could be useful in relating protein pattern changes to physiopathological events influencing the reproductive sphere.