Asexual sporulation in the fungus Aspergillus nidulans is controlled, in part, by a central regulatory pathway composed of the brlA, abaA, and wetA genes. The coding region of each of these genes was fused, in frame, to the threonine-inducible alcohol dehydrogenase promotor then stably incorporated into the A. nidulans genome at the argB locus. Misscheduled expression of each of these developmental genes interfered with normal growth and sporulation. Expression of brlA or abaA terminated vegetative growth and led to anomalous deposition of wall material at the hyphal apex and septa. brlA alone induced the formation of phialide-like structures and the production of conidia.