Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a major cause of severe neonatal jaundice in Nigeria, but not all G6PD-deficient babies become jaundiced. Neonatal jaundice not attributable to G6PD deficiency nor to any other known aetiology is also common. In an effort to explain these two facts, we have measured the levels of the three enzymes G6PD, glutathione peroxidase (GSHPX), and glutathione reductase (GSSGR) in 38 jaundiced newborns, 26 control newborns, and 44 normal adults, all of them males. We could not yet prove an additive effect of GSSGR or GSHPX deficiency with G6PD deficiency in causing jaundice. There was no evidence that low levels of GSHPX per se are associated with jaundice. However, jaundiced newborns with normal G6PD had significantly lower levels of GSSGR than control newborns with normal G6PD. These data suggest that a relatively low activity of GSSGR, a riboflavin-dependent enzyme, may predispose the red cells to accelerated destruction in the neonatal period.