Glanzmann's thrombasthenia (GT) is an autosomal recessive bleeding disorder due to a deficiency or abnormality of glycoproteins (GPs) IIb and IIIa, but its genetic basis remains to be determined. We analyzed the genes for GPIIb and 3'GPIIIa in 3 patients with GT and in 7 control subjects by Southern blot. No large deletions or insertions were detected in these genes in any patient with GT. Furthermore, the GPIIb and GPIIIa mRNAs derived from the platelets of patients with GT could be amplified using the reverse transcriptase-polymerase chain reaction (RT-PCR). This finding indicates that the mRNAs of the patients with GT are considered to be normally transcribed. The molecular defects of the GPIIb.