IntroductionGH activity may be involved in male reproductive function. A common genetic polymorphism in the gene encoding the GH receptor (GHR) results in deletion of the entire exon 3 sequence (GHRd3 isoform). The short GHRd3/d3 isoform seems more sensitive compared with full-length receptors (GHRfl/fl).AimTo investigate the associations between GH activity, evaluated by exon 3 GHR polymorphism, and serum IGF1 vs reproductive hormones, semen quality, and pre- and postnatal growth in healthy young males (n=838, mean age: 19.4 years).ResultsCompared with GHRfl/fl homozygous individuals (n=467) GHRd3/d3 homozygous individuals (n=69) tended to have larger semen volume (3.2 (2.4–4.3) vs 3.6 (2.6–4.7) ml, P=0.053) and higher serum inhibin-B levels (208 pg/ml (158–257) vs 227 pg/ml (185–264), P=0.050). Semen quality, levels of gonadotropins, testosterone, estradiol, sex hormone-binding globulin, and IGF1 were not associated with GHRd3 genotype.A twofold increase in serum IGF1 was associated with a 13% (4–23) increase in calculated free testosterone (P=0.004). By contrast IGF1 was inversely associated with serum inhibin-B (P=0.027), but showed no associations to semen quality. GHR genotype and serum IGF1 were not associated with size at birth or final height.ConclusionsGHRd3 polymorphism seemed only to have a weak influence on male reproductive function of borderline significance. The sensitive GHRd3/d3 genotype may slightly increase testicular function, as evaluated by semen volume and levels of inhibin-B, but does not seem to influence Leydig cell steroidogenesis. GHR genotype did not influence pre- and postnatal growth.