One hundred-word speech samples of alcoholic and schizophrenic subjects were examined in order to relate characteristics of these samples to the differential predictability of (a) alcoholic speech under drug vs. non-drug conditions (LSD-25), and (b) schizophrenic and alcoholic speech, using the cloze procedure. The deleted words in the samples were identified as to grammatical form class and frequency of usage, and these characteristics were related to predictability. Additionally, changes in predictability as the speaker continued to speak were studied. In the alcoholic speech passages, content words were harder to predict than function words, and decline in predictability under the drug was associated with a loss in content words rather than function words. The differential predictability of content and function words found in normal speech was not marked in schizophrenic speech. Predictability rose as the alcoholics continued to speak, both in drug and non-drug conditions, but dropped in schizophrenic speech.