Although magnesium is involved in many biological process and it is found higher levels in semen than serum, its role in human semen has not been elucidated. This investigation was conducted to evaluate the relationship between premature ejaculation and the levels of seminal magnesium. The levels of magnesium, zinc, copper, and selenium were evaluated with an atomic absorption spectrophotometer in serum and seminal plasma in 3 groups of men: (a) normal sperm parameters (15) (b) oligoasthenozoospermia (15), and genuine premature ejaculation (9). There were normal serum and semen levels of all the elements in the three groups, but significantly lower seminal plasma magnesium levels in men with premature ejaculation. The hormonal profile, body mass index (BMI) had no association with premature ejaculation. Decreased levels of magnesium gives rise to vasoconstriction from increased thromboxane level, increased endothelial intracellular Ca2+, and decreased nitric oxide. This may lead to premature emission and ejaculation processes. Magnesium is probably involved in semen transport. More research into the role of magnesium in the male physiology of reproductive tract, especially its association with premature ejaculation, is advocated.