This article examines a particular dramatic technique Ionesco uses to produce avant-garde humour. The Rumanian-born playwright chooses a real situation to start from and substitutes one element of the situation for something else, while retaining the rest. The characters react just as they would in the original situation – and therefore inadequately as far as the ,,substitution situation" is concerned. This technique explains why Ionesco's characters always keep a stiff upper lip even when they are faced with the most absurd events. The article illustrates this technique by giving selected examples from Ionesco's dramatic works.