In a 25-month prospective study of diarrhoeal disease in 236 hospitalized Filipino children under 12 years of age, a potential enteropathogen was detected in 235 cases (> 99%). Viruses, found in 169 cases (72%), were the predominant pathogens. Most of the virus infections [164 (69%) of the patients] were of rotavirus and 80% of these were in children under 2 years of age. Rotavirus infection was most prevalent in the cold months. Astrovirus and calicivirus were observed for the first time in the Philippines. Entero-invasive Escherichia coli (13% of patients), Salmonellae (6%) and Shigellae (3.4%) were the commonest bacterial enteropathogens. Cryptosporidium was detected in only six patients. Fever and vomiting, although significantly more prevalent in cases of bacterial diarrhoea than in viral, were not sufficiently sensitive or specific to be used to distinguish the two forms of diarrhoea. Presence of faecal leucocytes (> 5/higher-power field) proved highly sensitive (90%) and specific (84%) in detecting bacteria diarrhoea but reliance on this sign alone would have led to the misdiagnosis of one third of bacterial diarrhoeas.