Abstract. We analyzed intrusions of the Moon in the deep space view of the Advanced Microwave Sounding Unit-B on the NOAA-16 satellite and found no significant discrepancies in the signals from the different sounding channels between 2001 and 2008. Earlier investigations, however, had detected biases of up to 10 K by using simultaneous nadir overpasses of NOAA-16 with other satellites. These discrepancies in the observations of Earth scenes cannot be due to non-linearity of the receiver or contamination of the deep space view without affecting the signal from the Moon as well. As major anomalies of the on-board calibration target and frequency shifts of the local oscillator were not present, either, the most obvious reason for the degrading photometric stability is radio frequency interference in combination with a strongly decreasing gain. By means of the chosen example we demonstrate the usefulness of the Moon for investigations of the performance of microwave sounders in flight.