Chronic bladder pain syndrome is a chronic disabling disorder characterized by chronic pelvic pain, pressure or discomfort perceived to be related to the urinary bladder accompanied by at least one other urinary symptom such as persistent urgency or frequency in the absence of an identifiable cause. Chronic bladder pain syndrome severely decreases an individual's quality of life and represents a significant financial burden to those affected by it. Currently, multifactorial pathogenesis is assumed including endocrine-involvement, pelvic floor muscle irregularities, immunologic aspects and chemical causes. Corresponding to the wide spectrum of presumptive triggers, a large number of therapeutic approaches are propagated, however most are associated with limited effectiveness. Thus, treatment of BPS is a challenge and the ideal therapy remains to be elucidated. Microorganisms such as Chlamydia trachomatis, Ureaplasma urealyticum and Mycoplasma genitalium remains a challenge so that these organisms may well be involved in the pathogenesis of chronic bladder pain syndrome. The investigators hypothesise that doxycycline orally for 4 weeks, including therapy of the sexual partner, can significantly relieve symptoms in women with chronic bladder pain syndrome