Pharmacokinetic and clinical studies on DQ-2556, a new cephem antibiotic, in obstetrics and gynecology were performed and following results were obtained. Concentrations of DQ-2556 were determined in serum, internal genital organs and retroperitoneal exudate after single intravenous administration (i.v.) or drip infusion (d.i.v.) of 1.0 g. Serum levels following i.v. were approximately 30 micrograms/ml at 1 hour, 14 micrograms/ml at 3 hours 30 minutes, and concentrations in internal genital organs including oviduct, ovary, endometrium, myometrium, cervix uteri and portio vaginalis reached approximately 50% to 70% levels of serum concentration. The mean concentration (n = 6) in the retroperitoneal exudate after d.i.v. of 1.0 g following radical hysterectomy were about 20 micrograms/ml, 23 micrograms/ml, 14 micrograms/ml and 8 micrograms/ml at 1 hour, 2 hours 30 minutes, 4 hours 30 minutes and 6 hours 30 minutes, respectively. In clinical trials, DQ-2556 (2.0 g b.i.d. for daily dose) was given in 5 patients with gynecological infections such as pyometra (1 case), salpingitis (1), retroperitoneal space infection (2), pelvic peritonitis (1). The clinical results were evaluated as good in 3 cases and poor in 2 cases including a case with salpingitis infected by Pseudomonas aeruginosa and the other with pelvic peritonitis caused by Methicillin-resistant Staphylococcus aureus. Bacteriologically, 11 organisms were isolated from patients, and eradication rate was 54.5%. Neither side effect nor abnormal laboratory test result was observed. Thus, DQ-2556 appears to be effective for gynecological infections, and the good results were supported by good penetration of the compound into tissues of internal genital organs and retroperitoneal exudate after i.v. or d.i.v.