Obsessive-compulsive disorder (OCD) has been successfully treated with proserotonergic agents for some years. Clomipramine was the first drug used, but several clinical trials have been conducted more recently to assess the antiobsessional efficacy of selective serotonin reuptake inhibitors (SSRIs). The aim of this study was to compare the antiobsessional efficacy of three SSRIs, fluvoxamine, paroxetine, and citalopram. Thirty obsessive-compulsive patients without comorbid axis I diagnoses except for tic disorder as assessed by DSM-III-R criteria gave informed consent and were recruited consecutively; they underwent a 10-week randomized treatment with fluvoxamine, paroxetine, or citalopram. Ratings were performed under blind conditions every 2 weeks from baseline to the end of the study and by the Yale-Brown Obsessive-Compulsive Scale, the National Institute of Mental Health-Obsessive-Compulsive Scale, the Clinical Global Impressions Scale, and the Hamilton Rating Scale for Depression. Quantitative and qualitative analyses of the antiobsessional efficacy of the three drugs were completed with analysis of variance with repeated measures and survival analysis. The results showed no significant differences between the three treatments. The preliminary conclusions drawn from this study concern the interchangeable antiobsessional effects of different SSRIs, although further studies of "cross-response" to these drugs are needed.