By means of mathematical apparatus of a model of frequency lexical structure the structure of repetitions was studied in association flows of 10 healthy persons, 10 patients with sequelae of closed craniocerebral injury, and 10 schizophrenics. In comparison to healthy persons in those after the brain injury the number of repetitions was increased and the distances between the first and the last use of the repeated words were significant. In schizophrenic persons the repetitions of the words were situated at the local portions of association flows. The structure of repetitions in these association flows was close to that of the usual connected text by the general quantitative norms. Such structure of repetitions should be explained by the presence of a parasitical system of connections between the words equivalent by its strength to usual rational connections in a meaningful text.