The antimicrobial activities of n-butyric acid and its derivatives against Salmonella Typhimurium and Clostridium perfringens were studied. n-Butyric acid and its derivatives (monobutyrin and a mixture of mono-, di-, and tri-glycerides of butyric acid) were added at different concentrations (ranging from 250 to 7,000 mg/kg to a media inoculated with either Salmonella Typhimurium or C. perfringens. The antimicrobial activity of butyric acid against C. perfringens was measured at 2 bacterium concentrations and 2 inoculations involving ambient aerobic or anaerobic conditions. The most effective antimicrobial activity for Salmonella Typhimurium was observed with n-butyric acid, with 90% inhibition rate at a concentration of 1,500 mg/kg. Although minimal inhibition for Salmonella Typhimurium was observed with butyric acid glycerides, lipase addition to a mixture of mono-, di-, and triglycerides of butyric acid increased (P < 0.01) antimicrobial activity of these derivatives. Antimicrobial activity of butyric acid and its derivative against C. perfringens was higher when using a moderate initial inoculation concentration (10(5)) compared with a higher initial concentration (10(7)) of this bacterium. At a lower inoculation of C. perfringens (10(5)), >90% inhibition rate by all butyric acid glycerides was observed with prior aerobic inoculation at 2,000 mg/kg, whereas using anaerobic inoculation, only 50% monobutyrin maintained >90% inhibitory effect at 3,000 mg/kg. The antimicrobial effect of monobutyrin against C. perfringens was generally higher (P < 0.01) for 50% monobutyrin than for 100% monobutyrin. Either a mixture of butyric acid derivatives or 50% monobutyrin decreased (P < 0.01) C. perfringens in a media containing intestinal contents whereas only 50% monobutyrin decreased (P < 0.01) Salmonella Typhimurium within a media containing cecal contents from mature Leghorns. These results show that n-butyric acid and 50% monobutyrin could be used to control Salmonella Typhimurium or C. perfringens in poultry species.