Thirty-one samples of mothers' milk were analysed by neutron activation analysis for the concentrations of Mo, As, Mn, Zn, Cu 1.5 to 3 months post-partum. Group I consisted of 6 mothers having infants with neonatal obstructive jaundice and exhibited lower mean values of Cu and Mn at 0.18 microgram/g and 11.7 micrograms/g as compared with 16 control subjects with 0.34 microgram/g Cu and 23.0 micrograms/g Mn;Mo levels were approximately twice as high (12.2 micrograms/g) as the control values (6.4 micrograms/g); Zn and As were grossly comparable. Group II consisted of 9 mothers who had delivered infants with either a congenital hydrocephalus (n = 7) or meningomyelocoele (n = 2), exhibited a mean Cu level of 0.27 microgram/g, Zn 1.7 micrograms/g, Mn 25.3 micrograms/g and As 0.45 microgram/g. These findings are discussed in the light of the patho-physiology of the congenital anomaly of the infant.