A subtractive‐microwave‐holographic technique is described in this letter. This technique appears to be novel in that it displays only the difference of the two dissimilar microwave fields. The effect is achieved by making use of the phase reversal which occurs when a contact print is made of the microwave hologram. The technique was demonstrated by subtracting the microwave image of a coin from that of three coins. To show the practicability of the technique, it was applied to the diagnosis of a plasma discharge. The fact that this method can eliminate the masking effects scattered by the glass envelope and its supports is a substantial improvement over other microwave diagnostic tools.