The aim of the study was to assess the effect of olanzapine treatment of schizophrenic patients on cognitive functions measured with neuropsychological tests. Experimental measures were performed before starting treatment, after six weeks and after 4-12 (mean 6 months) of olanzapine treatment. The improvement in all groups of psychopathological symptoms of schizophrenia was found, the effect on negative symptoms being more marked with longer duration of olanzapine administration. Treatment with olanzapine resulted in significant improvement of psychomotor speed and auditory learning, in lesser extent influenced working memory functions. The improvement of cognitive functions after olanzapine, especially of auditory memory and learning was more marked with longer duration of treatment.