A study was carried out of 332 babies suffering from severe neonatal jaundice who were admitted to the General Hospital, Kuala Lumpar, Malaysia. Of the 332 neonates, 51 were premature and 281 were full-term babies, 178 (110 Chinese, 58 Malay, 9 Indian and 1 European-Pakistani) had bilirubin levels of 20 mg% or higher, requiring exchange blood transfusion. Of the Chinese neonates, 23 (20.9%) had G6PD deficiency, 9 (8.2%) had Hb Bart's and 2 (1.8%) had an abnormal haemoglobin, one Hb Q and one fetal variant. Among the Malay infants, 10 (17.2%) had G6PD deficiency, 7 (12.1%) had Hb Bart's and 10 (17.2%) had abnormal haemoglobins (four had Hb E trait, one had Hb K and Bart's in addition to Hb E, three had Hb CoSp with Hb Bart's, one had Hb Q and one Hb Tak). One of the nine Indian neonates had G6PD deficiency and one had Hb S trait. The one European-Pakistani baby was a carrier of Hb D Punjab. In addition to G6PD deficiency, abnormal haemoglobins seem to have contributed to the high incidence of severe neonatal jaundice in Malaysia. The mean activities of GP, GR and GR after stimulation with FAD were higher, while the mean activity of PK and mean level of reduced glutathione were lower than in normal cord bloods. The percent increase of GR after FAD stimulation was significantly lower; fewer in this group had increases above 20% than in normal cord blood. The possible significance of the findings is discussed.