Fc gamma receptors (Fc gamma Rs) are glycoproteins on platelet surface that bind IgG-containing immune complexes. However, excessive binding of immune complexes leads to platelet activation and thrombosis or increased platelet clearance and thrombocytopenia. In this study, Fc gamma R transcripts in platelets and megakaryoblastic cell line (Meg-01) were investigated using specifically designed oligonucleotides and a new quantitative in situ hybridization assay. Platelets and Meg-01 cells were found to express only Fc gamma RII transcripts. Of Fc gamma RIIA mRNA isoforms (Fc gamma RIIA, B and C), Fc gamma RIIA mRNA predominates in these cells. Platelets and Meg-01 cells contain both alternative spliced forms of Fc gamma RIIA mRNA, those with and without the transmembrane (TM) exon and both forms were present in near equal amounts. In contrast, Fc gamma RIIA transcript with the TM exon predominates in neutrophils and monocytes, suggesting that the splicing of the TM exon is under lineage-specific control.