A detailed study of the calcifuge Lupinus Iuteus L. (yellow lupin) has been carried out in an attempt to explain its poor performance in the presence of high concentrations of rhizosphenc calcium. Plants were grown on two different calcium regimes, 1 or 15 mol m– Ca and, after an establishment period, measurements were made of the rate of leaf extension, final length of the leaflets and the leaf gas exchange. In addition, the distribution of calcium within the leaf tissue was investigated. At 15 mol m–3 Ca, leaflet length at full expansion was reduced as a consequence of reduced extension rate and a decline in cell wall extensibility. Transpiration in excised leaves, assayed gravimetrically, was significantly reduced in plants grown in high calcium. Similar results were also obtained from gas exchange measurements. Analysis of A/C, curves indicated that in plants grown in high [Ca] there was a substantial reduction in net assimilation over a range of concentrations of CO2 X-ray microanalysis revealed that a large amount of cal cium delivered in the xylem sap is retained in the mesophyll tissue, and most of that reaching the epidermal tissue is not found in the guard cells but in the cells adjacent to them, which in this species are not anatomically distinct as ‘subsidiary’ cells.