An agar phantom with wide application in rf heating was developed. The phantom consists of 4 wt./wt. % agar powder, 0.1 wt./wt. % NaN3, 0-0.6 wt./wt. % NaCl, and 95.9-95.3 wt./wt. % water. The conductivity sigma (S/m) of the phantom was independent of frequency at 1-40 MHz, being sigma = 1.74 chi + 0.207 at 23.5 +/- 1 degrees C, where chi is the concentration of NaCl (wt./wt.%). The permittivity was nearly equal to 81 in the range of 5-40 MHz and 0-0.6 wt./wt.% of NaCl. The density and the heat capacity of the phantom were 1.02 X 10(3) kg/m3 and 1.00 kcal/kg degree C, respectively. The phantom had sufficient mechanical strength to permit construction of a torso 60 cm high. With the addition of a preservative, the phantom could be used for experiments on heating, without degeneration, for over one year.