Seminalplasmin, the major basic protein of bull seminal plasma, is a secretory protein of the seminal vesicles.

From the experimental results of three independent methods: (1) indirect immunofluorescence employing monospecific anti-seminalplasmin-IgGs, (2) cell-free translation of poly(A)+ RNA from seminal vesicle and testicular tissue, as well as (3) Northern analysis of poly(A)+ RNA of the latter tissues with a synthetic seminalplasmin-specific antisense DNA probe, it is concluded that the biosynthesis of seminalplasmin occurs in seminal vesicles but not in testis.