Steroid hormones including oestradiol have been identified as non-genetic factors that may influence plasma homocysteine. In advanced assisted reproduction, plasma oestradiol levels fluctuate markedly during the treatment cycle starting with normal followed by sub- and then supra-physiological levels. Because of the diverse harmful effects that hyperhomocysteinaemia has been associated with, it is imperative to understand how it may be manipulated during assisted reproduction. A total of 30 women undergoing treatment for infertility were recruited and followed through an advanced assisted reproduction cycle. Blood samples were analysed for oestradiol, homocysteine, vitamin B12, red cell folate and plasma folate during each phase. All patients had normal vitamin B12 and folate levels. Predictably, oestradiol showed marked changes as patients progressed through each treatment phase. However, there were no corresponding significant fluctuations in plasma homocysteine. Oestradiol concentration does not influence plasma homocysteine in women with normal vitamin B12 and folate levels undergoing advanced assisted reproduction.