Propranolol pharmacokinetics among different genotypes of CYP2D6 was compared in this study. The Chinese (Han) population consisted of 44 healthy unrelated individuals living in southern Taiwan. Endonuclease tests based on polymerase chain reaction were used to determine C/T188 genotypes of CYP2D6 in leukocyte deoxyribonucleic acid. Based on codon 188 genotypes, subjects were categorized into three groups: homozygous C/C188 (n = 13), heterozygous C/T188 (n = 14); and homozygous T/T188 (n = 17). Each subject was given a 40 mg propranolol tablet. Blood samples were drawn before and 12 hours after propranolol administration to measure propranolol and 4-hydroxypropranolol. Three genotypes showed distinct time profiles of plasma propranolol and 4-hydroxypropranolol. The area under plasma concentration curve values (mean +/- SEM), were 322.0 +/- 40.8, 481.6 +/- 77.5, and 766.1 +/- 92.8 nmol.hr/L, respectively, for C/C188, C/T188, and T/T188 subjects (p < 0.05). The 48-hour excreted amount of 4-hydroxy-S-propranolol-O-glucuronide, but not 4-hydroxy-R-propranolol-O-glucuronide, was significantly higher for C/C188 than for T/T188 subjects (p < 0.05). This study shows a different propranolol disposition in Chinese subjects of different CYP2D6 genotypes.