Mammalian fertilization includes highly regulated biochemical interactions: binding of seminal plasma proteins to the sperm surface during ejaculation, interaction of sperm surface proteins with oviductal epithelial cells, sperm capacitation, gamete recognition, primary binding of the sperm to the ovum, etc. Spermadhesins, sperm binding proteins of seminal plasma, play roles in all these events. The plasma membrane of spermatozoa undergoes extensive remodeling when sperm mixes with seminal plasma proteins at ejaculation. Some proteins of seminal plasma become sperm-coating agents. Two types of interactions could be involved in this process: (i) the interaction of proteins with the sperm membrane, (ii) mutual interactions between protein components. The second type of interactions is the subject of the present communication. Proteins of boar seminal plasma have been shown to be present mostly as aggregates of different composition and binding properties. Mutual interactions of proteins of boar seminal plasma likely to form aggregates were investigated by gel chromatography and affinity chromatography on immobilized spermadhesins. The protein composition of boar seminal plasma fractions adsorbed to immobilized spermadhesins was found to correspond to that of aggregated forms of seminal plasma proteins. Mutual interactions of isolated proteins were tested by gel chromatography and by specific antibodies against spermadhesins. The results obtained confirmed the existence of complex formation between spermadhesins of the AQN and AWN families, as well as between proteins involved in the formation of heterodimer PSP I/PSP II. Aggregated forms of spermadhesins are likely to be physiologically important in fertilization.