The parmacokinetics of Cefoxitin were studied after an i.v. administration of 15 mg/kg body weight in 17 patients with terminal renal impairment, 10 of which were undergoing 6 hr hemodialysis sessions. The average pharmokinetic parameters obtained from this kind of patient were the following: alpha = 2.88 hr-1 beta = 0.18 hr-1 K12 = 1.43 hr-1 K21 = 1.04 hr-1 K13 = 0.53 hr-1 Vc = 8.23 l Vp = 11.61 l Vdss = 19.84 l. The amounts of the antibiotic in the central and peripheric compartments are established together with the amount of the antibiotic eliminated as a function of time. The pharmacokinetic parameters are significantly different from those established in the period between dialysis sessions, and thus, the elimination constant reaches a value of 0.28 h-1. The degree of plasma protein binding of Cefoxitin is 41.46% during the hemodialysis sessions. A dosage regimen is programmed as a function of the pharmacokinetic parameters established for this kind of patient. It is recommended that an i.v. dose of 15 mg/kg body weight should be administered at the beginning and end of each dialysis session lasting 6 hours, when the periods between the sessions are 48 hours.