By using serial dilution technique in broth the authors have ãetermined the minimum inhibitory concentration of the 150 strains of Salmonella typhi isolated in their totality from blood cultures in the presenoe of ampicillin and hetacilin. An average of the bacteriostatic concentration 0,545 mcg/ml for the ampicillin and 0,720 mcg/ml for the hetacilin was obtained.