SummaryThealcRpositive control gene is necessary for the expression of bothalcA(coding for alcohol dehydro‐genase ADH I.) andaldA(coding for aldehyde dehydro‐genase, AldDH) inAspergillus nidulans.Using a clonedalcRprobe and Northern blots analysis we show that: (1)alcRitself is inducible; (2)alcRinducibility depends on the expression of thealcRgene Itself; and (3)alcRis subject to carbon catabolite repression and its expression Is controlled by the negatively actingcreAwide specificity gene. The repression ofalcRis sufficient to explain the cariaon catabolite repression of ADH I and Al