In rats, the effects of a 4-week supplementation of a fibre-free elemental diet with 100 or 200 g Plantago ovata seeds/kg was compared with that of the husks and wheat bran. The seeds increased faecal fresh weight up to loo%, faecal dry weight up to 50% and faecal water content up to 50%. The husks, at the high concentration only, were more effective and wheat bran less effective. Length and weight of the small intestine were not greatly affected by the seeds, but both variables increased significantly in the large intestine. The husks had more pronounced effects, especially in the small intestine, and wheat bran almost no effect. Faecal bacterial mass as estimated from the 2,6-diaminopimelic acid output was increased to the greatest extent by the seed-containing diet and by the high concentration of husks, but to a lesser extent by wheat bran. Faecal and caecal protein content was enhanced by the seeds and wheat bran, but to a lesser extent by the husks. Total acetate in caecal contents or faeces was highest on the seeds and husks diet and not elevated by wheat bran. Total faecal bile acid excretion was stimulated and P-glucuronidase (EC 3.2.1.31) activity reduced by both Plantago uvuta preparations, but not by wheat bran. Mucosal digestive enzyme activities were inhibited to different degrees by all dietary fibres in the jejunum, and sometimes activated in the ileum. These results suggest that Plantago ovata seeds are a partly-fermentable dietary fibre supplement which increases stool bulk; metabolic and mucosa-protective effects are also probable.Plantago uvata: Dietary fibre supplement Dietary fibres from natural or semi-synthetic sources have gained increasing attention as a supplement to the normal Western diet, which is poor in bulking substances, and as a prophylactic or therapeutic treatment of large bowel disorders (Dreher, 1987). Plantago ovum husks, often referred to as ispaghula (husks) or as psyllium (which is a misleading term as nearly all the commercially-available drug derives from Piantago ovafa Forsk. and not from Plantago psyllium L.) and wheat bran are widely used and well-investigated examples. Both compounds increase stool weight (Stevens et al. 1988), but have rather opposite physicochemical properties regarding solubility and water-binding capacity Van Soest, 1984;Englyst et al. 1989).Another fibre source, less well known, is Plantago ovata seeds. In contrast to the husks which consist only of the hulls of the seeds, the seed preparation includes the kernel together with the hulls. The water-holding capacity of the seeds is intermediate between that of the husks and wheat bran (Sosulski & Cadden, 1982;Struthers, 1986; LengPeschlow, 1990). Clinical studies with a Plantago ovata seed preparation indicate that this compound increases stool weight and reduces intestinal transit time in healthy volunteers (Heckers & Zielinsky, 1984) and augments stool frequency, stool mass, and water content in constipated patients (Solter & Lorenz 1983;Marlett et al. 1987). Symptoms in irritable bowel patie...