Molecular mutations of the giucose-Cphosphate dehydrogenase (G6PD) gene and clinical manifestations of neonatal jaundice in 112 male and 50 female Chinese neonates with G6PD deficiency were studied. In the 112 males, the nucleotide (nt) 1376 (G-T) mutation was the dominant type (50.0%), followed by nt 1388 (G-A) (16.1%), nt 493 ( A S ) (8.0%), nt 1024 (C-T) (6.2'70), nt 95 ( A S ) (5.4%), nt 392 (G-T) (1.8%), nt 487 (G-A) (1.8%), nt 871 (G-A) (0.9%), and nt 1360 (C-T) (0.9%). The nt 871 variant has not been reported in Taiwan before. The occurrence rates for nt 1376, nt 1388, nt 493, nt 95, and nt 1024 mutations in the 50 females were 44.0%, 18.0'70, 12.0%, 6.0%, and 6.0%, respectively. The type of G6PD mutation in 10 male and 7 female neonates has not been identified yet. Although G6PD deficient neonates had higher frequency of phototherapy than G6PD normal neonates In both sexes, a significant difference in the prevalence of hyperbilirubinemia (peak bilirubin 215.0 mgldi) between G6PD deficient and normal neonates was found only in males. Further analysis showed that duration of phototherapy was longer in G6PD deficient male neonates than In the control group, while the outcome of phototherapy was better in subjects with non-nt 1376 mutations than subjects with the nt 1376 mutation. Most (78.3%) of the 23 G6PD deficient neonates who subsequently suffered from neonatal hyperbilirublnemia carried the nt 1376 mutation. The results of this study Indicate that the nucieotlde substitution at 1376 is the most common and important mutation for G6PD deficiency in Chinese neonates in Taiwan.