& Abstract Endometrial sonographic and color doppler features can be used to predict the occurrence of pregnancy in natural or stiumlated cycles. Implatation will usually onlytake place if the endometrium has reach a certain stage of vascularisation and development. Th e aim of this study was to evaluate endometrial devalopment – endometrial thickness and refl ectivity , subendometrial, endometrial and uterine perfusion, after hyperbaric oxygenation, using transvaginal color doppler. During a three years period  women with unexplained infertil ity were entered into a randomised study. Th e patients were treated in multiplaced HAUX chamber at pressure of , ATA during  minutes,  days consecutively begining with day th of menstrual cycle.Th e evaluation of eff ects of hyperbaric oxygen therapy was carried out by transvaginal color doppler sonography which was continuously used starting from th day of menstrual cycle untyl the ovulation in the cycles when the therapy was applied , one month before and one month after the therapy. Folliculometry in the cycles when hyperbaric oxygen therapy at , ATA was applied, indicated an excellant response of endometrium. Th ickness of endometrium at the time of ovulation was , ± ,mm. Desirable quality of endometrium was signifi cantly better in the cycle when HBO therapy had been applied (p< ,). Th e doppler fl owmetry of the uterine arterys indicated that the uterine blood vassel resistance was slightly higher than expected. Mapping of subendometrial blood vessels in the cycles covered by hyperbaric oxygen therapy showed the intensive capillary network of en dometrium with low resisstance Ri< ,. Th e oxygen used under higher pressure – oxygen as a drug , may have an extraordinary signifi cance for better outcome of pregnancy implantation by improving endometrial receptivity. If endometrial receptivity is conditioned by adequate vascularisation and oxygenation, then hyperbaric oxygen therapy is the treatment of choice. KEY WORDS: endometrial receptivity, hyperbaric therapy, infertility Hyperbaric Oxygenation as a Possible Therapy of Choice for Infertility Treatment