The number of subjects who practice recreational breath-hold diving is increasing; therefore there is a growing need to know the adaptations that this sport could have on the health of the participants. They are exposed to an increased hyperbaric pressure and low temperature that cause change in arterial blood gases and induced a human diving response which includes increased arterial blood pressure, reduced cardiac output, bradycardia and peripheral vasoconstriction. Start on the matter that these adaptations are still not fully understood, we decided to investigate some biomarkers that should be involved in this disorders starting to analyse Hypoxia-inducible factor 1 alpha (HIF-1a). We enrolled in our study 31 healthy free divers from different part of Sicily, aged 41,86 ± 11,41, weight 77,52 ± 11,30 kg, height 175,19 ± 6,13 cm, who practiced this activity for more than 5 years. We asked them to perform 5 consecutive dives at 20 meters, without permanence on the bottom, with free recovery between the different dives. A baseline venous blood sample was taken immediately after surfacing from the 5th dive (less than 3 minutes). The samples were stored to -80 until the analysis were done using ELISA method. The results showed that comparing HIF-1a value before and after the dives, there were an increase in the concentration that started from 158,43 pg/ml and be at end 246,06 pg/ml. In conclusion, the Hypoxia-inducible factor 1 alpha can be considered co-responsible for various phenomena, certainly not with pathological destinies, but rather working with "adaptation" phenomena to this type of activity. These are just the preliminary results that need further investigations to be confirmed.