The regulation and pattern of gene expression for cytochrome P4504C1 was measured in the fat body of adult females of the cockroach, Blaberus discoidalis. The level of CYP4C1-mRNA was high at adult emergence but disappeared after 4 days of adult life. In starved females, CYP4C1-mRNA levels declined by day 4 but increased steadily thereafter; by 25 days, the levels were nearly twice those observed at eclosion. Both the rapid early disappearance of the transcript and the starvation-related increase failed to occur following decapitation. Allatectomy also prevented the disappearance of CYP4C1-mRNA at day 4, and treatment of decapitated females with methoprene (JHA) stimulated a 70% decrease in transcript within 24 h. Injection of synthetic Blaberus hypertrehalosemic hormone (HTH) increased CYP4C1-mRNA by six-fold in the fat body of both intact and decapitated females. CYP4C1-mRNA in the fat body of males did not respond to JHA treatment. The dynamics of CYP4C1-mRNA in the fat body of females could be explained based on an inhibition of CYP4C1 expression by JH that was overcome by HTH.