Basic and clinical studies on cefclidin (CFCL), a newly developed injectable cephem antibiotic, were carried out in the field of surgery, and the following results were obtained.<BR>1. Antibacterial activity MIC₅₀/MIC₉₀ (μg/ml) of CFCL against clinical isolates from surgical infections, of Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, were 12.5/100, 0.1/0.78., 0.1/0.39, and 3.13/12.5, respectively. Antibacterial activity of CFCL against S.aureus was as strong as those of ceftazidime (CAZ). However, the activity of CFCL against E.coli and K.pneumoniae, was equal or superior to activities of CAZ, and CFCL showed the most powerful activity against P.aeruginosa among all drugs tested.<BR>2. Penetration into bile and ascites: Biliary levels of CFCL were determined in 6 patients. The mean peak level of CFCL after the administration at 1 hour after dosing of 1g (i.v.) was 17.4μg/ml. No accumulation of CFCL was recognized in bile after the repeat administration. Meanwhile, the mean peak level of CFCL in ascites on for 5 patients reached 30.6μg/ml after the dosing of 1g (i.v.)<BR>3. Clinical results: CFCL was administered to 24 patients with surgical infections. The clinical responses were excellent in 3 cases, good in 11, fair in 6, poor in 3, unevaluable in 1 and the overall efficacy rate was 61%. Bacteriological responses were eradicated in 4 cases, partially eradicated in 4, persisted in 2, replaced in 5 and the overall eradicated rate was 60%.<BR>No adverse reaction was noted. Abnormal laboratory findings were recognized in 6 cases but these abnormal changes returned to normal ranges after the termination of dosing.