Ceftriaxone effectively inhibited 332 out of 452 (73.45%) bacterial strains in vitro tests. 291 out of 365 (79.69%) gram negative and 41 out of 87 (47.12%) gram positive strains were inhibited. The tests showed ceftriaxone to be more effective than cephalothin, cephotaxime, cephuroxime, cephamandol and cephoxitin. Kinetic tests showed that cephtriaxone has a plasmatic half life of 7.25 hrs. 24 hours after administration of a 1000 mg venous bolus the drug was still present in the blood. Urinary elimination over a 24 hr. period amounted to means 486.8 mg (48.68%). The drug has liquor transfer capacity. 37 of the 38 patients treated showed complete clinical or clinicobacteriological cure. Improvement was noted in the 38th.