The demand for glycine to satisfy normal growth during early life is considerable and most has to be made endogenously. The extent to which adequate glycine is available can be assessed by measuring the urinary excretion of 5-L-oxoproline. The excretion of 5-L-oxoproline at 6 weeks of age for infants in Trinidad of African, Indian or mixed parentage (398 mumol/mmol creatinine) was significantly greater than for infants born in England of Caucasian parentage (194 mumol/mmol creatinine). There was no relationship between 5-L-oxoproline excretion and either sex or pattern of feeding. There were significant inverse relationships between 5-L-oxoproline/creatinine and birth weight, and head circumference either at birth or 6 weeks of age, suggesting that limited availability of glycine is associated with poorer growth before and after birth. For a group of infants born in England of Indian parentage, excretion of 5-L-oxoproline (155 mumol/mmol creatinine) was not different to infants of Caucasian parentage, but significantly less than infants born in Trinidad. The demonstration that 5-L-oxoproline/creatinine was similar in infants born in England, regardless of parentage, shows that the differences between England and Trinidad are related to environment and are unlikely to be accounted for by genetic differences or ethnicity.