Abstract
One of the main characteristics of idioms is their fixedness. In spite of that, we frequently encounter different kinds of varieties of their use both in written and in spoken language.
Most frequently, these varieties consist in a substitution of one of the components by another one, more or less synonymous. The introduction of my paper is dedicated to the types of these varieties, the following part focuses on the impact of the substitution of one of the idiom's components on it's meaning.
The difference between varieties and transformations of idioms is also explained briefly. Finally, I present the results of a research into the frequency of ocurrence of particular varieties of chosen portuguese idioms.