Twenty-four female patients suffering from gynaecological malignancies and scheduled for internal and external irradiation of the pelvic area (pelvic dose 5000 cGy) were selected for a study on prevention of intestinal side-effects by live Lactobacillus acidophilus cultures. The patients were randomised into two groups. Both groups received dietary counselling recommending a low-fat and low-residue diet during radiotherapy. The control group received dietary counselling only. The test group received 150 ml of a fermented milk test product supplying them with at least 2 X 10(9) live Lactobacillus acidophilus bacteria daily and 6.5% lactulose as substrate for the bacteria. The results indicated that the test product appeared to prevent radiotherapy-associated diarrhoea. However, flatulence was increased probably due to lactulose ingestion in the test group.