To study clinical and biological tolerability, 114 chronically constipated patients of both sexes, aged 18-70, without any organic alteration of the colon, received lactitol over a period of one or two months. Clinical tolerability was found to be good by 80 per cent of patients and biological tolerability excellent. Clinical efficacy was found correct for 80 per cent of patients with a dosage of 20 g (single dose in the evening). All patients, except one, agreed with the packaging and the taste of the product.