Pelvic inflammatory diseases are usually caused by sexually transmitted microorganisms, as are Neisseria gonorrhoeae and Chlamydia trachomatis, either alone or associated with endogenous flora of the lower genital tract, as with other gram-positive and gram-negative anaerobic and aerobic bacteria [1, 2]. METHODS The aim of the study was to estimate the effect of three broad-spectrum combinations of antimicrobial therapy in the treatment of pelvic inflammatory diseases in hospitalized patients. METHODS We analysed the therapeutic success of some antimicrobial therapies in 154 patients with pelvic inflammatory disease, who were treated in the Narodni Front Hospital of Gynaecology and Obstetrics in Belgrade, during 1992 and 1993. Three drug therapies were applied. The combination of Ceftriaxon plus Doxycycline was given to 51 women. Fifty five women were treated by a combination of Gentamycin plus Clidamycin, and 48 women were treated by a combination of Gentamycin and Metronidazole. RESULTS The therapeutic success after the application of the three different antibiotic therapies was recorded in 139 of 154 women (90.26%). Of 136 patients with uncomplicated pelvic inflammatory diseases, the therapeutic success was noted in 129 (94.85%) individuals, while of 18 women with tubo-ovarian abscess therapeutic success was recorded in 10 (55.56%) patients. Of 51 women treated by the combination of Ceftriaxon plus Doxycycline, the therapeutic success was observed in 46 (90.19%) patients. Fifty five women treated by the combination of Gentamycin plus Clindamycin, the therapeutic success was noted in 50 (90.19%) subjects. Of 48 women, treated by the combination of Gentamycin plus Metronidazole, the therapeutic success was found in 43 (89.58%) women. No statistically significant difference was found among the applied antibiotic therapies (p > 0.05). Of 18 women with tubo-ovarian abscess 8 were operated on. Of these 8 women in 6 patients hysterectomy with bilateral salpingo-oophorectomy was performed and in two women unilateral salpingo-oophorectomy was carried out. CONCLUSIONS Pelvic inflammatory diseases are often of polymicrobial aetiology. In 43 patients we found two types of bacteria in the cervical culture. The therapeutic success was achieved by these three antibiotic therapies. It was 90.26%, the therapeutic success in the treatment of pelvic inflammatory diseases by Ceftriaxon plus Doxycycline was noted in 90.19% of patients. The therapeutic success of antibiotic therapy with Gentamycin plus Clindamycin was obtained in 90.91% of patients. The success of antibiotic therapy with Gentamycin plus Metronidazole was recorded in 89.59% of patients. Our results are similar to those of other authors [3, 4, 6, 7]. No statistically significant difference was found among the applied antibiotic therapies. CONCLUSIONS An early diagnosis and an aggressive treatment may prevent serious sequelae of this increasingly common sexually transmitted disease. The antibiotics should be of antimicrobial broad spectrum. Good effects can be best reached by a combined antibiotic therapy. Duration of parenteral administration of antibiotics should be several days and for at least 48 hours after the patient's defervescence.