Pregnancy, delivery, and postpartal metabolic control was monitored biochemically in five patients (22-38 years of age) with clinically, enzymatically, and genotypically established classical galactosaemia and good dietary compliance. Three of the patients performed breast feeding of their newborns. Monitoring parameters were galactose-1-phosphate and galactitol concentrations in erythrocytes and urinary excretion of galactose, galactitol, galactonate, and lactose. During pregnancy, a small but steady increase of renal metabolite excretion rates was observed. After delivery, a moderate transient increase of metabolite concentrations with peak values within the first week post partum occurred, irrespective of breast feeding. Altogether, there was no evidence for clinically or subclinically significant changes of metabolic control during pregnancy, delivery, or lactation. In conclusion, a specific metabolic monitoring is apparently not required in pregnant galactosemic women, and breast feeding of the nongalactosemic offspring can be recommended.