Progress in labour is governed by the presentation, size and position of the baby, the shape, tone and compliance of the birth canal and probably the most important factor, the power of the uterine contractions. Failure to progress in labour is a significant clinical problem and contributes to one fifth of all Caesarean sections. However it is a problem which is difficult to treat and present day methods of management have not been shown to reduce the rates of operative delivery for these labours. Indeed only 51.1 % of women who received treatment for prolonged labours over a five year period at St Mary's Hospital had a normal delivery as compared with 76.6% who progressed spontaneously; this suggests significant scope for an improvement in management of labours which are failing to progress. Clearly before improved management strategies can be devised a better understanding of what maintains the effectiveness of contractions during labour is needed. There is circumstantial evidence to suggest that during labour episodes of maternal apnoea and changes in uterine/myometrial blood flow as a result of uterine contractions, maternal positions and maternal dehydration contribute to a situation where the myometrium is exposed to intermittent periods of hypoxia and re-oxygenation. Therefore the aims of this study were to determine the effects of hypoxia and re-oxygenation on human myometriai contractility, to ask whether oxygen free radicals modulate contractility and attempt to link changes in the oxygenation of myometrium with oxygen free radical generation. Hypoxia directly inhibited both spontaneous and agonist induced contractions in the myometrla from pregnant and non-pregnant women. The effects of short episodes of hypoxia were reversible and repeated episodes of hypoxia/reoxygenation initially increased contractility of spontaneously contracting myometriai strips from pregnant women. Myometriai contractions were significantly affected by oxygen free radicals and antioxidants. No direct evidence for the generation of oxygen free radicals within myometria during periods of hypoxia/re-oxygenatlon could be demonstrated, however, the development of future experiments to investigate more fully this possibility were discussed. Finally the results of preliminary experiments designed to explore methods of investigating the relationship between oxidative stress and human labour, using ex vivo, were discussed. In conclusion although the mechanisms which maintain effective uterine contractions In labour are yet to be fully elucidated the results of this thesis support the possibility that episodes of hypoxia and re-oxygenation influence uterine contractions in vivo and this effect in part may be modulated by endogenous free radicals and endogeous and dietary antioxidants. It is hoped this study will be a stepping stone to future work which will improve the care of women in labour and promote normality in child birth.