Chinese data on the polymorphic metabolism of debrisoquine, metoprolol, codeine and mephenytoin were collected and re-analysed using a meta-analysis method. There were no significant differences in the incidences of poor metabolizer (PM) between the separate series of debrisoquine, metoprolol and codeine, which are the three probe drugs reflecting the same enzyme polymorphism. PMs were detected at low frequencies for debrisoquine (1.20%; 95% confidence interval, CI: 0.67-1.98%), metoprolol (0.72%; CI: 0.29-1.49%) and codeine (0.48%, CI: 0.01-2.68%). The overall estimate of PM was 0.95% (CI: 0.60-1.42%) based on the 2427 determinations of all three probe drugs. The overall mean of PM of mephenytoin was 14.32% (12.26-16.38%) in the 1117 subjects. In summary, the present meta-analysis determined the accurate incidences of the genetic deficiency of S-mephenytoin 4'-hydroxylase (cytochrome P450 2C19) and debrisoquine hydroxylase (cytochrome P450 2D6) in Chinese populations.