Root nodules of Lupinus albus (L.) cv. Multolupa were subjected to short- and medium-term stresses by lowering rhizosphere temperature from 25 to 16°C (2 h), detopping plants (3 h), darkening plants (21 h) or exposing roots to 20 mol m–3 KNO3 for 4 d. All experimental treatments produced increases in oxygen diffusion resistance, compared with control plants. These correlated with structural changes in the nodule cortex, which is described in detail for the first time. The most noticeable change is the occlusion of intercellular spaces by a glycoprotein which was identified using the monoclonal antibody MAC236. This glycoprotein was also found surrounding bacteria in intercellular spaces of the cortex of control nodules.