Platelet-activating factor (PAF) modulates the functions of eosinophils, which play an important role in allergic inflammation, through a specific receptor(s) expressed on the cell surface. We compared expression levels of mRNA for the PAF receptor (PAF-R) in peripheral blood eosinophils from atopic asthmatic patients with those from normal healthy subjects using a relative quantification method based on the reverse transcription-polymerase chain reaction (RT-PCR). We found that the levels of PAF-R mRNA in eosinophils from the patients were significantly higher than those in normal subjects. These results suggest that the increased expression of PAF-R in eosinophils may be relevant to the pathogenesis of atopic asthma.