The Aspergillus nidulans brlA gene encodes a transcriptional regulator of central importance in controlling conidiophore development. I have determined the effects of mutations in other developmental regulatory genes on expression of a brlA-lacZ fusion gene. Deletion of brlA reduced beta-galactosidase levels by half and led to delocalization of enzyme accumulation. The medA26 and abaA2 developmental mutations led to overexpression of the fusion gene without altering spatial specificity. In contrast, the stuA1 mutation did not affect the timing or levels of brlA expression during induction, but instead resulted in spatial derangement of expression. These results and the phenotypes of the mutants suggest a model in which subsets of morphogenetic loci are controlled by differing levels and combinations of regulatory gene products, which are themselves determined by interactions among the regulatory genes.