To detect the level of fasting plasma homocysteine (Hcy) in patients with oligospermia and/or asthenospermia and to investigate its clinical significance.Semen quality analyses and fasting plasma Hcy determination were performed for 86 infertility patients (21 with oligospermia, 32 with asthenospermia and 33 with oligo-asthenospermia) and 19 normal fertile volunteers. The results were compared.The level of plasma Hcy was significantly higher in the infertility patients than in the normal controls (P < 0.05) and negatively correlated with sperm concentration (r = -0.433, P < 0.01), the percentage of grade a sperm (r = -0.303, P < 0.05) and the percentage of grade a+b sperm (r = -0.339, P < 0.01).The increased level of human plasma Hcy directly or indirectly affects spermatogenesis and correlates negatively with oligospermia and/or asthenospermia.