The functional status of the Fallopian tubes in patients with unexplained infertility (UI) was evaluated with radionuclide hysterosalpingography (RN-HSG). The rate of bilateral tubal occlusion with RN-HSG in women with UI (3/18 = 16.7%) was considerably higher than in a group of fertile and male-infertile women (0/28 = 0%), implying that a number of cases with UI might be associated with functional rather than anatomical tubal defects. RN-HSG is a simple, innocuous and potentially useful method for assessing functional tubal occlusion, and it might give a better understanding of the functional status of the tubes in UI.