The effects of diarrhoea on the activities of brush-border disaccharidases namely lactase (EC 126.96.36.199), maltase (EC 188.8.131.52) and sucrase (EC 184.108.40.206) of Sprague-Dawley strain albino rats were induced in the rats with mannitol while secretory diarrhoea was induced with Salmonella typhimurium after an initial treatment with streptomycin. The activities of the enzymes were significantly reduced by diarrhoea. The extent of reduction in enzyme activity varied in the different segment of the small intestine in all the groups. The jejuno-ileal region had more changes in enzyme activities than in the duodenum. Higher activity levels were observed for maltase than for lactase. In the osmotic diarrhoea model, lactase activity was significantly lowered (P < 0.05) in the experimental group from day 5 to 10. Maltase activity on the other hand was significantly lowered (P < 0.001) at the peak of diarrhoea. Sucrase activity was also lowered significantly (P < 0.025) in the experimental animals within the first 10 days of diarrhoeal induction. In the secretory diarrhoea model, lactase activity was similar in all the experimental groups except for the streptomycin-salmonella-treated groups and control (P < 0.05). Higher lactase activity levels were observed in the secretory diarrhoea model compared to level in the osmotic diarrhoea model. Maltase activity levels were also lowered significantly (P < 0.05) in the experimental animals. Streptomycin had no effect on the activity of maltase.