OBJECTIVE To determine if the purported deaminase inhibitors diphenyliodonium chloride (DIC) and thymol reduce the growth and survivability of Campylobacter. RESULTS Growth rates of Campylobacter jejuni and Camp. coli were reduced compared to unsupplemented controls during culture in Muellar-Hinton broth supplemented with 0.25 micromol DIC or thymol ml(-1) but not with 0.01 micromol monensin ml(-1) or 1% ethanol. Recovery of Camp. jejuni and Camp. coli was reduced >5 log(10) CFU from controls after 24 h pure culture in Bolton broth supplemented with 0.25 or 1.0 micromol DIC ml(-1) or with 1.0 micromol thymol ml(-1). Similarly, each test Campylobacter strain was reduced >3 log(10) CFU from controls after 24 h mixed culture with porcine faecal microbes in Bolton broth supplemented with 0.25 or 1.0 micromol DIC ml(-1) or with 1.0 micromol thymol ml(-1). Treatments with 0.25 micromol thymol ml(-1), 0.01 micromol monensin ml(-1) or 1% ethanol were less effective. Ammonia production during culture or incubation of cell lysates was reduced by 0.25 or 1.0 micromol DIC ml(-1) but only intermittently reduced, if at all, by the other treatments. CONCLUSIONS Diphenyliodonium chloride and thymol reduced growth, survivability and ammonia production of Camp. jejuni and Camp. coli. CONCLUSIONS Results suggest a potential physiological characteristic that may be exploited to develop interventions.