SUMMARYAn assessment was made of the efficacy of aβ‐galactosidase, obtained fromAspergillus nigerand added to intact milk, in decreasing lactose malabsorption and intolerance. Sixteen adult patients with malabsorption and intolerance to this sugar were studied in a double‐blind crossover studyvs.placebo. A 5‐hour hydrogen breath test was used to assess malabsorption of lactose contained in 400 ml milk. When compared with placebo, the addition of exogenous lactase to intact milk caused a statistically significant reduction in the maximum breath H2concentration (P<0.01) and in the cumulative H2excretion (P<0.005). In the same way, the cumulative index for gastrointestinal intolerance was significantly lower (P<0.005) after the ingestion of lactase‐added milk. This study demonstrates that enzyme replacement therapy, withβ‐galactosidases obtained fromAspergillus niger, is effective in decreasing lactose malabsorption and its consequent intolerance in adult subjects with lactase