Pentosan polysulfate sodium (PPS) was compared with placebo for the symptomatic therapy of interstitial cystitis in a double-blind, multicenter study. A total of 110 patients were enrolled and treated for three months. In this study, overall improvement of greater than 25 percent was reported by 28 percent of the PPS-treated patients and by 13 percent of the placebo-treated patients (p = 0.03). The investigators' overall evaluation provided similar results, 26 percent vs 11 percent in favor of PPS (p = 0.04). Improvement in pain and pressure to urinate also favored PPS over placebo and approached statistical significance (p = 0.07 and 0.08). The incidence of adverse reactions was 6 percent in the PPS-treated group and 13 percent in the placebo-treated group. All adverse reactions were minor, and treatment was discontinued by 1 patient in the PPS group and 2 in the placebo group. In this study, PPS was found to be significantly more effective than, and equally as safe as, placebo.