Allatostatins of the YXFGLamide group were discovered in cockroaches through their capacity to inhibit juvenile hormone biosynthesis. Here, we assess the occurrence of preproallatostatin (preproAST) mRNA in the brain and midgut of adult females of the cockroach Blattella germanica, and estimate brain and midgut preproAST mRNA levels during the first reproductive cycle. Reverse transcription polymerase chain reaction (RT-PCR) shows that brain preproAST mRNA levels increase slightly during the gonadotrophic cycle, and remain high during ootheca transport. In the midgut, preproAST mRNA levels decline around the middle of the gonadotrophic cycle. The pattern of allatostatin expression in gut tissues suggests that these peptides play roles related to feeding and nutrition. Our results have shown that synthetic allatostatins inhibit hindgut motility and activate midgut alpha-amylase secretion. In addition, injected allatostatins inhibit food consumption, which might be connected to the above activities.