Boar sperminogen was purified from the acid extracts of the washed epididymal spermatozoa by gel filtration through a Sephadex G-100 column, followed by preparative SDSPAGE. The 32 kDa sperminogen band was sliced oat frnrn the preparative SDS-PAGE and 32 kDa sperminogen was eluted from the gel matrix. The purified 32 kDa sperminogen was subjected to amino acid composition analysis. The amino acid composition of the 32 kDa boar sperminogen showed significant differences from that of either boar proacrosin or β-acrosin, which signifies that 32 kDa sperminogen might not be a breakdown product of proacrosin-acrosin system and that the 32 kDa sperminogen is a different protein from proacrosin-acrosin system.