Photosynthesis, transpiration and carbon isotope ratios of 11 mistletoes and their hosts were measured in central and eastern Australia to test hypotheses regarding similarity of photosynthetic rate between host and parasite and significance of host xylem carbon as a contributor to parasite carbon gain. Differences in photosynthetic rates of mistletoes and their hosts were not statistically significant, although most mistletoes had slightly lower photosynthetic rates and much higher transpiration rates than their hosts. Uptake of carbon dissolved in the xylem sap of the host was estimated from the discrepancy between observed and predicted carbon isotope ratios. Dividing xylem carbon gain by measured transpiration yielded a mean ± SE xylem carbon concentration of 10 ± 2.0 mM (...)