A new method for measurements of ultralow currents in the audio‐frequency range (from dc up to over 104Hz) has been developed. The combined use of a ferromagnetic current transformer and of a superconducting flux transformer together with a rf‐biased SQUID allows measurements of currents as low as 10−14A. A detailed circuital analysis and considerations on the input impedance of the device are presented. The agreement between predictions and experiments is quite good. The measured noise level beyond the low‐frequency region keeps at values typical of commercial SQUID’s.