Two types of superconducting gravity gradiometers have been developed. Both employ superconducting test masses suspended by niobium diaphragms whose motions modulate persistent currents in superconducting loops. A current signal proportional to the gravity gradient is detected by a 19 MHz SQUID. The balancing of common acceleration has been verified experimentally for both systems. A gradient sensitivity better than 2×10−10 s−2 Hz−1/2 with a baseline of 10 cm is expected of these gradiometers.