Fresh yogurt has been proposed as a milk substitute for lactase-deficient patients. We investigated the possibility that a dried, low-fat milk fermented by yogurt microorganisms would be effective. Processing of a fermented milk by spray-drying led to a powder with persistence of lactase activity (11.7 units/g) without storage at 4 degrees C and stable at room temperature (20-23 degrees C). The tolerance and absorption of 10.5 g of lactose in a volume of 150 ml was studied in 25 Gabonese lactase-deficient children aged 5-14 years in the form of a standard humanized milk formula followed 1 week later by the powdered fermented milk formula. Results of the breath hydrogen test showed that in 24 of 25 cases, lactose absorption was normal with a maximal rise of hydrogen over baseline of under 13 ppm after ingestion of the powdered fermented milk. The rise was above 20 ppm in the 25 children with the same load of lactose in the form of the standard formula and one-third had symptoms of lactose intolerance. This powdered fermented milk preparation should be considered as a valid approach in programs of nutritional support targeted to countries with a high prevalence of lactase deficiency.