A clinical investigation was made among workers in a sewage treatment plant and age matched controls not exposed to sewage. Acute incidences of fever and eye symptoms were found in about 50% of the exposed population. Serum immunoglobulins, white blood cells and thrombocytes were elevated in the exposed group. A higher percentage of increased levels of C-reactive protein and fibrinogen degradation products was found in the exposed group. Although no definite cause-effect relationship can be established the responsible agent in the environment could well be endotoxins.