This study was undertaken to investigate the possible carry-over effect on elderly long-term patients of bulk-forming products containing stimulant type laxatives. Thirty-six patients received magnesium hydroxide daily for a mean period of 10 months prior to the study, and 23 patients received bulk laxatives containing cassiae senna daily for a mean period of 13 months prior to the study. The pre-study laxatives were randomly changed either to magnesium hydroxide or to bulk laxatives. In the patient group receiving a bulk-forming product containing stimulant type laxative long-term prior to the study, the need for additional stimulant laxatives during the pure bulk laxative (3.0 vs. 3.8/4 weeks, NS) or magnesium hydroxide treatment (2.6 vs. 2.7/4 weeks, NS) was not more frequent and the frequency of defaecation was not lower than in the patients (during bulk laxative 11.2 vs. 9.3/4 weeks, NS and during magnesium hydroxide 12.0 vs. 13.7/4 weeks, NS) who received long-term magnesium hydroxide treatment prior to the study. Thus, our data indicated no carry-over effect after the use of bulk-forming laxatives containing senna for 13 months in elderly long-term patients.