Masses and radii of eclipsing brown-dwarfs and low-mass stars (circles with error bars, as labeled) compared to theoretical mass-radius relations (lines). The lines correspond to isochrones of 0.5 (upper orange lines) and 5 Ga (lower blue lines), respectively. The dashed lines are calculated for isolated brown-dwarfs and low-mass stars. The plain lines include the effect of irradiation with T_eq = 1800 K. The dash-dotted lines include irradiation and account for a 50% coverage of the photosphere with low-temperature spots (see text). A 5 Ga isochrone for isolated brown dwarfs/M stars from Baraffe et al. (2003) is shown for comparison (dotted line).