Recently, the YAMIK sinus catheter (YAMIK) has been reported to be a useful therapeutic device in the treatment of sinusitis. The present study was conducted to compare its delivery of either a normal saline (NS) or a betamethasone solution (0.4 mg/ml) into the paranasal sinuses of 25 patients (39 sides) with chronic sinusitis. The following parameters were evaluated: (1) subjective nasal clinical symptoms (nasal discharge, nasal obstruction, postnasal drip and headache), (2) X-ray photographs (ethmoid and maxillary sinuses) and (3) cytokine levels (IL-1beta, IL-8 and TNF-alpha) by enzyme-linked immunosorbent assay. The total nasal symptom scores significantly decreased after the first therapy, and the total X-ray photograph scores significantly decreased after therapy with either NS or the betamethasone solution. In both NS and betamethasone patients, the levels of IL-1beta and IL-8 had significantly decreased by the 3rd and 2nd weeks after therapy, respectively. In contrast, the TNF-alpha level decreased after the first therapy with betamethasone solution and remained unchanged after therapy with NS. These findings suggest that evacuation of the pathological effusions in sinuses may exert a beneficial effect by reducing the levels of IL-1beta and IL-8, and we speculate that removal of pathological effusions from the sinuses may provide treatment through different mechanisms than those that occur in treatment with betamethasone.