Although the specific contribution of CRTH2 in allergic inflammation thus is inconsistent in studies using mice with targeted gene disruption, the findings of the present study are congruent with the notion that CRTH2 represents an eosinophilotactic receptor and provide strong support for the concept that CRTH2-signaling in vivo is an important molecular step in the pathogenesis of allergic asthma. The gene discussed is PTGDR2; the disease is allergic asthma.