The effect of acute ethanol intoxication (ethanol 33%, i.v.) on day 4 of pregnancy (at 9 o'clock a.m.) upon the initial stages of implantation in mice was investigated. The pregnant animals (treated and controls) were killed in the afternoon and in the evening of day 5 of pregnancy (at 30 and 36 hours after ethanol administration). After histological proceeding, the pregnant uteri were microscopically examined, using the following criteria: the position of embryos, the stage of embryos differentiation, the aspect of uterine epithelium, the decidual reaction and the presence of oedema. The results obtained are analysed and compared with some literature data and with our previous results. Some apparent contradictions between the data presented and those previously reported, require new investigations.