The Widal slide agglutination test was evaluated as a rapid diagnostic test in typhoid fever patients at the Infectious Diseases Hospital, Jakarta, Indonesia from 1980-1982. The results of the test can be available within 45 minutes of patient admission. The study showed that, among 229 patients with Salmonella typhi-positive typhoid fever and 179 control fever patients, when the Widal O antibody titer was greater than or equal to 1:20 the sensitivity was 53%, the specificity 98%, the positive predictive value 96%, and the negative predictive value 68%. A negative Widal test (O antibody titer less than 1:20) does not provide useful information, but when the O antibody titer is greater than or equal to 1:20 the clinician at the Infectious Diseases Hospital of Jakarta can be 96% certain that the patient has typhoid fever.