As Chomsky pointed out (1961), generalized transformations are the support of the recursivity of grammar. Among these, embedding trausformations by relativization are of special interest to the psycholinguist in that they illustrate a possible discrepancy between the acceptability and the well-formedness of sentences. Thus, they may shed light on the distinction between competence and performance, Consider the following sentences (1) and (2), borrowed from Miller (1962). These two sentences are equally grammatical but (1) is harder to process and memorize than (2): (1) The race that the car that thepeople whom the obviously not very well dressed man called sold won was held last Stimmer.(2) The obviously not very well dressed man called the people who sold the car that won the race that was held last summer.The purpose of the present study is to compare the performances of French speaking children and adults who are required to produce sentences involving a relative transformation. It is assumed that the diflference in performance between öiir children and adults, especially differences in difficulty based on the nature of the material and differences in types of error, will permit us to give a relatively clear description of the mechanisms involved in such performance, and the corresponding heuristics.