ABSTRACT. Antibiotic therapy administered for treatment of gram-negative bacterial infections can exert a negative effect in the form of endotoxin shock. Therefore, a sterilization method that releases little endotoxin is required. This in vitro study aimed to compare the amounts of endotoxin released from Escherichia coli exposed to antibiotics (aminobenzylpenicillin, kanamycin, oxytetracycline, sulfadimethoxine and enrofloxacin) or ozone. The bacterial growth and amount of endotoxin released were measured at specific time points. Compared with antibiotic treatment, ozone sterilization induced release of smaller amounts of endotoxin from the bacteria. Moreover, no major differences were observed when ozone was used against the purified endotoxin. We conclude that compared with antibiotic treatment, ozone sterilization may release smaller amounts of endotoxin. KEY WORDS: Escherichia coli, endotoxin release, ozone.