Elevated plasma homocysteine is an independent risk factor for the development of many pathological states, but at present, there is only little information about its concentration in seminal fluid. It is also well known that folate plays an important role in the reproduction and that the treatment with folate antagonists impairs the reproductive functions in men. A previous study found that low seminal plasma folate concentrations are associated with low sperm density and sperm count and that folate concentrations in the seminal fluid correlate with blood plasma folate and homocysteine. The homocysteine, vitamin B12 and folate concentrations were significantly higher in men with normospermia than in men with azoospermia and oligoasthenospermia. Negative correlation between folate and homocystein in normospermia group was found. Low levels of homocysteine in the group with azoospermia may indicate decreased metabolic activity in the testes of these men.