The paper presents method of measuring the internal oxygen concentration of intact non-lignified plant roots with an oxygen sensitive Clark - type micro-electrode, also allowing the measurement of oxygen partial pressure without interference from electrolytic properties of the root tissue. The use of a motor driven micromanipulator generated continuous profiles of oxygen pressure across the roots. The method was used for measuring the radial distribution of oxygen partial pressures within primary roots of 7-12 days' old broad bean, (Viciafaba L. ssp. minor), pea (Pisum sativum ), and lupin (Lupinus angnstifolius L.) seedlings. It has been stated that anoxic conditions can exist in the meristematic root zone even under atmospheric concentration of oxygen outside the root. The axial oxygen partial pressure within the roots of the flooded seedlings decreased with the distance from the root tip. Flooding the soil reduced scattering of the results and "smoothed" the dependence of axial oxygen pressure on the distance from the root tip. It also lowered the values of axial oxygen partial pressure in the case of lupin which showed the highest axial oxygen partial pressures as compared to the other plant species studied.