Retrogenesis is claimed to be the process by which degenerating mechanisms in the brain, as found in Alzheimer's disease (AD), reverse the order of acquisition of functions, including language, in normal child development. In FAST (Functional Assessment Staging of Alzheimer's disease) stages of AD are translated into corresponding developmental ages. Humour, irony and sarcasm are communicative strategies linked to meta-linguistic abilities developed late in childhood. If found in the conversation of people with moderately severe AD according to FAST, this could be an indication of problems in the FAST scale and subsequently in the concept of retrogenesis concerning speech and language abilities. Comprehensive, open-ended, naturalistic conversations between three nursing home residents with moderately severe AD according to FAST and their professional care-givers were analysed with concepts developed in linguistics as to the occurrence of humour, irony and sarcasm. Although the data material was limited, the findings indicate an unexpected communicative competence of the three participants. This is a corrective to retrogenesis and a caveat for poor expectations of intelligible conversations with demented people for professionals and the people they advise. Implications for research strategies and for the general knowledge of communicative competence in AD are addressed in the discussion section, and possible ways of elucidating deterioration of speech and language abilities in AD are suggested.