Mass-radius diagram of the known transiting planets with R_p ≥ 0.4 R_Jup and M_p ≥ 0.1 M_Jup. Only systems with masses determined to better than 30% precision are included. Green diamonds indicate the solar system giant planets Jupiter and Saturn (from right to left). The three dotted lines display isodensity curves of 0.1, 0.5, and 1.5 g cm^-3. The position of TrES-4b as determined in this work is shown with a filled red square, to be compared with that (empty red square) derived by S09.