The application of a combined HPLC-RIA methodology to estimate immunoreactive PGE2 levels in two insect species, namely, males of the cricket Gryllus bimaculatus (Orthoptera, Gryllidae) and males and females of Blattella germanica (Dictyoptera, Blattellidae) is reported. From the results obtained, it can be concluded that, whereas in the crickets the presence of a female does exert a stimulating effect on the PGE2 levels of the male, in cockroaches nonsignificant differences on PGE2 contents were observed among virgin and mated individuals under the conditions assayed, thus suggesting that the biosynthetic pattern of this prostanoid in the cricket studied cannot be extended to the case of the Dictyoptera.