Using Reverse Transcription-Polymerase Chain Reaction, an expression profile for the Avian Sex-specific gene on the W chromosome (ASW) was established. All female tissues extracted from the brain, gonad, pancreas and breast muscle, between stage X (Eyal-Giladi and Kochav, 1976) and 1 year post hatch expressed ASW. Tissues extracted from male chickens did not express ASW. This expression profile of ASW is consistent with a role in controlling gonadal differentiation or a secondary sexual characteristic, such as sexually dimorphic growth. To test the hypothesis that ASW plays a role in sexually dimorphic growth, mixed sex chimeras carrying female cells were analyzed for ASW expression. Additionally, the body weights of those mixed sex chimeras were compared to body weights of male same sex chimeras and male and female White Leghorns and Barred Plymouth Rocks. The data collected were consistent with the hypothesis that ASW has a role in controlling sexually dimorphic growth.