Background: Transition metal ions, such as iron, can make electron donations to oxygen forming superoxide or hydrogen peroxide, which is further reduced to an extremely reactive hydroxyl radical that induces oxidative stress. The purpose of the present study was to design a system that could easily detect and reliably measure the ferrous oxidation associated to oxygen radical reactions in the sperm samples. Methods: A total of 64 sperm samples from 11 men who had normal semen parameters and proven fertility and 53 male partners of couple experiencing primary infertility, were included in the study. The semen samples from oligoasthenoteratozoospermic patients was divided on the basis of spermatic parameters into moderate, when the sperm concentration was ≥5 × 106/ml and in severe when the concentration was <5 × 106/ml. The evaluation of the ferrous oxidation was performed measuring the formation of iron complexes between ferric ions and thiocyanate anions by spectrofluorimetry. Results: The concentration of the ferric thiocyanate complex ions was significantly higher in pathological sperm samples (137.6 ± 10.8 μmol/l in moderate oligoasthenoteratozoospermic, 170.0 ± 25.4 μmol/l in severe oligoasthenoteratozoospermic and 155.4 ± 7.3 μmol/l in non-obtructive azoospermic men), when compared with both infertile noormozoospermic (92.4 ± 10.7 μmol/l) (P<0.015) and with samples from fertile men (76.3 ± 6.2 μmol/l) (P<0.005). No significant differences were found in the concentration of ferric thiocyanate complex among the different pathological groups when compared to each other and in infertile noormozoospermic patients when compared with the samples from men of proven fertility (P=0.168). Accordingly, an inverse correlation was found between the concentration of the ferric thiocyanate complex and total motility, progressive motility and morphology. Conclusions: This preliminary study shows that the method proposed detect quickly and reliably measures the ferrous oxidation associated to oxygen radical reactions in the sperm samples.