This study is being conducted at the University Hospital of Lund University in Malmo, Sweden, in collaboration with the U.S. National Institute of Child Health and Human Development. The study will try to identify genetic causes of impaired sperm production and male infertility. It will focus on the possible role of the MTHFR and CBS genes, which regulate absorption and metabolism of the vitamin, folate in infertility. If the nutritional intake or metabolism of this vitamin is related to male infertility, then this cause of infertility would be potentially curable.

Fertile and infertile men between 20 and 45 years of age may be eligible for this study. Criteria include the following:

• Fertile men: men whose partners are younger than age 40 and are attending Lund University prenatal clinic; who have fathered one or more pregnancies and who stopped birth control to achieve the present pregnancy; who achieved the present pregnancy in less than 12 months of unprotected intercourse.
• Infertile men: men referred to the Scandian Andrology Centre whose infertility is unexplained, whose partners are younger than age 40 and who have had regular sexual intercourse without contraception for at least 12 months without achieving a pregnancy.

All participants will have the following tests and procedures:

• Complete a questionnaire providing information about their reproductive and medical history and recent dietary history;
• Provide blood samples for analysis of red cell folate, plasma folate, plasma homocysteine, plasma B12, and for genetic evaluation;
• Provide a semen sample for routine analysis, including volume, sperm concentration, sperm motility, and sperm morphology.

In addition, infertile men will undergo a physical examination and review of their medical records.