PurposePrevious studies have suggested the involvement of serum IGFs and IGFBPs in the regulation of the female reproductive system. Little is known of these peptides in the seminal plasma (SP) of men and their potential effects on fertility. We assessed SP levels of these peptides in infertile men with low sperm motility (asthenozoospermic; AZ) and low sperm counts (oligozoospermic; OZ), its effects on in vivo sperm motility, and whether aging affects these peptides.MethodsTwenty eight infertile men (AZ; n = 18 and OZ; n = 10) and 20 fertile normozoospermic (NZ) men were studied. Seminal plasma IGF-I, IGF-II, IGFBP-2, IGFBP-3 and PSA levels were measured, and spermatozoa mRNA transcript patterns were examined.ResultsAsthenozoospermic men had higher SP IGF-I, IGF-II, IGFBP-2 and PSA levels than NZ and OZ men (all P < 0.05), whereas SP IGFBP-3 levels were no different between the three groups. Sperm count positively correlated with SP IGF-I, IGF-II and IGFBP-2; sperm motility negatively correlated with SP IGF-II and IGFBP-2; and age correlated positively with SP IGF-II (all P < 0.04). The expression of IGF-I and IGF-II mRNA and mRNA receptors was detectable, but no variations in transcript levels were noted. ConclusionDecreased sperm motility, but not sperm count, in infertile AZ men is associated with increased SP IGF-I, IGF-II, IGFBP-2 and PSA levels. Changes in SP IGFs and their interactions with IGFBPs and IGF receptors, and PSA levels suggest a role of these SP peptides in modulating sperm motility and possibly prostate disease development in aging men.