- Acute infectious diseases of the gastrointestinal tract and food poisoning are problems of great importance in the Israel Defense Forces (IDF). They involve individual and epidemic morbidity, with impairment of health of individual soldiers and in the activities of units. Outbreaks of gastrointestinal infectious diseases must be reported to the IDF army health branch, which conducts epidemiological investigation. This study is based on data from yearly epidemiological reports for 1978-1989, and from a computerized database for the years 1990-1995. The incidence of outbreaks is characterized by an unstable trend. It was highest at the end of the 80's (68.3 per 100,000 soldiers on active duty) and lowest for the last 2 years (1994-1995, 36.3 per 100,000). The incidence of soldiers involved in food-borne outbreaks has been more stable, constantly declining during the course of the years. There was marked seasonality with a peak in the summer months. Sporadic morbidity was constant in 1990-1995, with a yearly attack rate of 60% in soldiers on active duty. Shigella strains were the leading cause of outbreaks until 1993, while in 1994-1995 their proportion decreased, with an increase in the proportion of Salmonella strains. As to Staphylococcus aureus, its role in causing food poisoning has been characterized by marked changes. Shigella sonnei replaced Shigella flexneri as the leading strain. 73.3% of outbreaks were small, with fewer than 40 soldiers involved, while 5.4% of outbreaks affected more than 100 soldiers. Outbreaks in which a bacterial agent was identified or which occurred in new-recruit bases were larger than those in which a bacterial agent was not identified, or which occurred in active field unit bases. In conclusion, the rates of infectious disease of the gastrointestinal tract are still high, although there has been a marked decrease since 1994. The incidence of outbreaks has also decreased, as well as the role of Shigella as a leading causative agent.