Prostaglandins are local transient hormones that mediate many biological activities, including pain and several aspects of female reproduction. Little is known about prostaglandin signalling during reproduction but on p. 839, Tina Tootle and Allan Spradling report for the first time that Drosophila egg maturation requires a cyclooxygenase (COX)-like activity. COX is the rate-limiting enzyme in vertebrate prostaglandin synthesis and COX inhibitors are widely used as painkillers. Using an in vitro egg maturation assay, the researchers show that the COX inhibitor aspirin halts follicle maturation. They also identify the Drosophila peroxidase Pxt as a candidate COX enzyme and show that maturing follicles in pxt mutant females (which are sterile) have defects in actin filament formation. The maturation of pxt follicles in vitro is stimulated by prostaglandin treatment, they report, and the expression of mammalian Cox1 restores the fertility of pxt mutants. Thus, the researchers conclude, prostaglandins promote Drosophila follicle maturation, making fly oogenesis a useful model for genetic studies on these important biological regulators.