The authors diagnosed lactose malabsorption by the breath hydrogen analysis in 11 premature and mature babies, in 16 infants and in 28 children between the ages of 3-18 years. All patients were treated with Galantase (beta-galactosidase). According to the results, Galantase is very effective in splitting of lactose of breast-milk, cow-milk and artificial formulas. Pathological hydrogen increase was not detected during the treatment.