Application of reverse transcription and the polymerase chain reaction to identify the Pl^A1 polymorphism as due to a nucleotide mutation leading to a Leu33Pro substitution in the integrin β3 subunit. Bases 56-408 of integrin β3 were enzymatically amplified from individuals who were homozygous Pl^A2 or heterozygous Pl^A1/Pl^A2 and analyzed on agarose tells. The enzyme is sensitive to the T→C change in the sequence at base 196 associated with the Pl^A2 polymorphism. Reprinted with permission from Newman et al. J Clin Invest. 1989;83:1778-1781.⁸⁴