The sensitivity and specificity of counterimmunoelectrophoresis using three antigenic preparations obtained from Salmonella typhi were compared with those of the Widal test in the serological diagnosis of typhoid fever. A veronal buffer extract yielded precipitation lines against 50 (96%) out of 52 sera collected from patients with typhoid but against none out of 62 sera obtained from control subjects who did not have typhoid. Less satisfactory results were obtained by counterimmunoelectrophoresis when two other preparations, a protein extract (Barber antigen) and an ultrasonic lysate, were used as the antigens. By Widal test the rate of detection in patients' sera was 73% and the false-positive rate for control sera 16%. It is concluded that in an area where typhoid is endemic counterimmunoelectrophoresis using veronal buffer extract as the antigen is superior to the Widal test for serological diagnosis of typhoid fever. An additional advantage of counterimmunoelectrophoresis is that results may be obtained on the same day that the serum specimens are received.